LCP Introduction To Liquid Crystal Polymers - Zeus
Technical PaperLCP Introduction ToLiquid Crystal PolymersARTICLE ––––––––––Written by:Kevin J. Bigham, PhD.Zeus Industrial Products, Inc.Keywords and related topicsBiocompatible plasticsCatheter braidingCatheter constructionLCPMonofilamentMRI �––––––Liquid crystal polymers (LCPs) present a special category of material which straddles theboundary between an ordinary solid and a liquid. From their first discovery in the laboratoryto the realization that liquid crystals also exist in biology, these unique molecules are nowomnipresent in a broad spectrum of modern-day applications. Different from typicalthermoplastics such as polyesters and other aromatic polymers, LCPs have significant higherorder structure particularly apparent in their liquid phase. This feature gives LCPs a host ofparticularly useful material properties such strength, dielectrics, chemical reactivity(resistance), and biocompatibility for medical applications. In this latter vein, Zeus hasintroduced LCP extruded as a monofilament fiber for use as vascular catheter reinforcementbraiding. As a non-metallic braiding, catheters made with LCP monofilament can be usedunder magnetic resonance imaging (MRI). This imaging technique precludes the use ofmetals, and to date, no widely accepted MRI-compatible catheter has been achieved. Includedhere is an overview of LCPs, their unique chemical structure and orientation, and theirrelevance in industry as thermoplastics. We compare LCP monofilament to other catheterbraiding materials including stainless steel and multifilament yarn. We show that LCPbraiding rivals stainless steel in several areas and offers improved catheter construction. Wepresent that catheters made with LCP monofilament braiding are poised to become the firstfully MRI-compatible catheters both for performance and manufacturability. 2016; 2018 Zeus Industrial Products, Inc.INTRODUCTIONLIQUID CRYSTALS: DISCOVERYLiquid crystal polymers are a unique class of materialthat only relatively recently has gained widespreadinterest. Liquid crystals, the building blocks of liquidcrystal polymers, blur the boundary between properties ofan ordinary liquid and a solid. These special moleculeshave even been found in biological molecules includingDNA and micelles. Yet, appreciation of their significancealmost did not happen. But where did these uniquemolecules come from? What is their origin? Once thoughtto be an unusual state of matter, liquid crystal polymers arenow thoroughly embedded in our daily lives. Today, thesespecial polymers are of greatest interest and utility in thearea of thermoplastics. From food containers tomechanical parts to monofilament fibers, liquid crystalpolymers have proven to be highly versatile – both inmolecular design and properties.The origin of liquid crystal study is typically tracedback to Austrian chemist and botanist Friedrich Reinitzer.In 1888, he observed and later wrote about the strangebehavior of a solid after exposing it to changingtemperatures. Using solid cholesteryl benzoate, Reinitzernoticed that at one temperature the solid became a hazyliquid, yet at a higher temperature, the hazy liquid becameclear [1]. When cooling the clear liquid, again Reinitzersaw the liquid pass through two different color formsbefore returning to the original white solid with which hebegan [1]. Reinitzer had observed two different meltingpoints for the same material – a phenomenon which shouldnot exist. Perplexed by his discovery, Reinitzer forwardedthe solid white material along with his findings to OttoLehmann, a physicist working out of Aachen in what isnow present day Germany.Turning Polymers Into Possibilities
LCP Introduction To Liquid Crystal Polymers Lehmann was better equipped to study the material thanReinitzer and expanded upon Reinitzer’s work. Lehmannplaced the material which he had received from Reinitzeron a microscope equipped with a heat stage and observedthe material while heating it [2]. Lehmann observed thefirst (intermediate) hazy liquid as the white solid meltedjust as Reinitzer had. He described seeing crystallites –multiple small crystalline formations with irregularborders. Lehmann realized that this first intermediate fluidappeared to be crystalline in nature and that it must in factbe a new state of matter [2]. After further studying andrefining his ideas, Lehmann named his discovery a liquidcrystal [2]. Lehmann’s (and Reinitzer’s) observationreceived significant attention at the time, particularly afterLehmann published his findings in 1900. Indeed, by theearly twentieth century nearly 200 other compounds werefound to show liquid crystal behavior. However, after thisinitial attention, no practicable application for this newdiscovery was forthcoming, and interest in this new area ofscience soon waned.While Reinitzer and Lehmann are routinely given noteas the originators of liquid crystal science, they were alsolikely aware of earlier work by fellow German WilhelmHeintz. This highly published and productive chemist haddone significant work on fatty acids. By 1850, Heintz hadnoted that certain natural fats had two different meltingpoints [3, 4]. His observations were nearly identical toReinitzer’s and Lehmann’s: As Heintz raised thetemperature of the fat substance he was analyzing, thesubstance first became cloudy, then fully opaque. Finally,the substance turned completely clear with continuedheating [3, 4]. Just as Reinitzer’s and Lehmann’s officialdiscovery in time garnered no real appreciation, so was thecase with Heintz’s observation on two melting points for asingle substance. This observation of two melting points,however, would later become fundamental to identifying aliquid crystal.THE NATURE OF THE LIQUIDCRYSTALWhat Reinitzer, Lehmann, and others had found was anew state of matter somewhere between a true solid and aliquid. The liquid crystal contained small elements whichappeared to be crystalline in nature but were suspended ina liquid phase. Also, unlike typical pure substances whichKevin J. Bigham, PhD.melt precisely at a given temperature, liquid crystalsexhibited two melting points. This liquid crystal new inbetween phase of matter was thus termed a mesophase.The individual molecules in the substance capable offorming a mesophase, or liquid crystal, are termedmesogens. These molecules are usually small to moderatesize organic molecules and arrange themselves in varyingdegrees of organization or order. However, not all of theseself-organizing molecules within the liquid crystalparticipate in the ordering thus giving the liquid crystal itsunique behavior as neither a solid nor a liquid. As anexample, gelatin is a substance which exhibits amesophase.Further developments in the study of liquid crystalsrefined their natural character. Two general types of liquidcrystal were determined: those that came about by heatinga solid and those that resulted from addition of a solvent.Liquid crystals that could be brought about by solvationare called lyotropic; those of the type that Reinitzer andLehmann discovered were the result of heating and arecalled thermotropic liquid crystals [5]. Thus, whenconsidering mesophases (liquid crystals), it is perhapsmore appropriate and for ease of understanding to view thechanging states or phases of the mesophase substance astransitions from solid to liquid crystal to liquid. Boththermotropic and lyotropic mesophase types would haveparticular importance in industry and biology.Making up the mesophase itself are the small organicmolecules within it. While not all molecules are capable offorming mesophases, the possibilities for mesogenicmolecule types are nearly limitless. Thus, mesogensusually have some degree of non-uniformity in theirstructure and connectivity of atoms; that is, they are notsymmetrical. This non-symmetrical nature implies that themolecules have some degree of directionality and thatcertain of their qualities or properties vary according to thisdirectionality. This directionality of properties is calledanisotropy. As an example, N-(4-Methoxybenzylidene)-4butylaniline (MBBA), the first synthetic liquid crystalmolecule, is asymmetrical and exhibits anisotropicproperties in its liquid crystal phase (Fig. 1). Conversely,molecules that are entirely symmetrical have propertiesthat do not vary based upon any directionality; they arecalled isotropic [6]. These descriptors of isotropy andanisotropy can be extended to higher forms of matter toinclude solids, liquids, and gases. The degree of isotropic 2016; this revision 2018 Zeus Industrial Products, Inc.2
LCP Introduction To Liquid Crystal Polymers and anisotropic character of the mesophase (liquid crystal)consequently dictates its behavior.While liquid crystals exhibit unique behavior differingfrom solids and liquids, they also show myriad charactereven among themselves and other liquid crystals. At theroot of the diversity of liquid crystals are the diversearrangements of their mesophase molecules whichcontribute to their micro-crystalline formations. Amongthe first to organize and classify the different types ofliquid crystals based on these arrangements was Frenchmineralogists and crystallographer Georges Friedel.Fundamentally, Friedel’s mesophase classificationfocused on symmetry as a primary explanation formesophase behavior [7, 8]. In 1922, Friedel proposed threeclasses based on the structure of the mesophase [7]. Sincethen, study has expanded the number and detail of liquidcrystal structure descriptions, a full description of which isbeyond the scope of this paper. This article, thus, will limitdiscussion of liquid crystal structures to isotropic (liquid),nematic, smectic A, smectic C, and crystalline (solid)forms.ABCFigure 1: Representative liquid crystal mesogen molecules.(A) N-(4-methoxybenzylidene)-4-butylaniline (MBBA), (B) 4methoxycinnamic acid, and (C) cholesteryl stearate (5Cholesten-3β-yl octadecanoate).The orientation of the mesogen molecules lies at theheart of liquid crystal functionality. Recall that the liquidcrystal lies in between the two fundamental states of liquidand solid. In a liquid, the mesogenic molecules becomearbitrarily oriented with no directionality and form anisotropic fluid (Fig. 2A) [5]. These liquid state moleculeshave no fundamental order, and this liquid phase isisotropic in nature. Conversely, in their solid state, thesesame molecules are highly ordered and closely packedwith almost no translational freedom (Fig. 2B). For liquidcrystals, however, the distinguishing feature is that theirKevin J. Bigham, PhD.mesogenic molecules – which are non-symmetrical innature – self-align along a definite axis; this axis is calledthe director (Fig. 3) [5]. This positional orientation alongthe director is the critical element for the formation ofnematic and smectic liquid crystal structures as well as ofthe solid (crystalline) phase [9]. The longer range order ofthe liquid crystal is typified by the director. Nematic liquidcrystal molecules, for example, maintain their directionalorientation but do retain some freedom of movementwithin the liquid crystal (Fig. 3A) [6]. Smectic mesogenicmolecules are arranged such that their principal axes are 2016; this revision 2018 Zeus Industrial Products, Inc.3
LCP Introduction To Liquid Crystal Polymers parallel with their centers of mass in one plane; these liquidcrystals exhibit positional as well as directional order (Fig.3B and C) [5]. The material properties of liquid crystalssuch as optical activity, magnetic, and electrical propertiesare thus anisotropic. These properties aid in distinguishingliquid crystals and are largely the result of the degree ofmesogen directionality [10]. For a liquid, which isisotropic, these properties show no variation regardless ofthe direction from which they are measured. Apart fromthermodynamics effects, the behavior of the liquid crystalis thus dictated by the pattern of mesogen alignment.A. Liquid (isotropic)B. Crystalline (anisotropic)Figure 2: Diagram showing the arrangement of mesogen molecules within asubstance. (A) Liquid (isotropic) and (B) crystalline (solid, anisotropic) forms.(Adapted from: Wang, X. J.; Zhou, Q. F., Liquid Crystalline Polymers. World Scientific:2004).A. nematicB. smectic AC. smectic CFigure 3: Diagram showing the arrangement of mesogen molecules within liquidcrystal types. Liquid crystal forms exhibit directional alignment of their molecules andare anisotropic. (A) Nematic liquid crystal showing orientational order, (B) smectic Aliquid crystal form, and (C) smectic C liquid crystal form. B and C possess orientationaland positional order. (Adapted from: Ermakov S, Beletskii A, Eismont O, Nikolaev V:Liquid Crystals in Biotribology: Synovial Joint Treatment. Cham: SpringerInternational Publishing; 2016).Kevin J. Bigham, PhD. 2016; this revision 2018 Zeus Industrial Products, Inc.4
LCP Introduction To Liquid Crystal Polymers TYPES OF LIQUID CRYSTALSAside from their asymmetrical nature, liquid crystalmaterials generally exhibit several other characteristics incommon. Like MBBA, mesogen features usually includerigidness along its longitudinal axis, a rod-like or ellipsoidmolecular (monomer) structure, strong dipoles, and areeasily polarized. These rod-like (calamitic) monomerspossess a hydrophobic non-polar end and a polarhydrophilic opposite end – a characteristic calledamphiphilic (Fig. 4A). Liquid crystals may also becomposed of disc-shaped molecules and bent-core orbanana-shaped molecules (Fig. 4B and C). Bent and discshaped mesogen molecules also have amphiphilic regionswhich facilitate their aggregation into liquid crystals justas rod-like mesogens [5].Distinguished from their monomeric composition,liquid crystals may form many differing simple andAcomplex shapes when in their liquid crystalline stateswhich effect their functional attributes. Rod-shaped(calamitic) liquid crystals can display a range ofmesophases including nematic and varying smectic formsdepending on the temperature (Fig. 5A) [6]. Disc-shaped(discotic) liquid crystals usually form nematic or columnlike structure phases (Fig. 5B) [6]. Bent-core mesogenscan display crystalline structures including nematic,smectic, and a range of their own unique banana liquidcrystal phases (Fig. 5C) [11]. Liquid crystal phases mayalso be composed of rod-like and disc-like moleculescombined into one complex structure [10]. This diversityamong monomeric mesogen types and subsequent selfassembly results in a nearly limitless number ofarrangement modes for these liquid crystalline structures.The concomitant properties of these liquid crystals havethus fostered a broad area of scientific research producingmany significant innovations.BCFigure 4: Representative liquid crystal mesogen molecules. (A) Rod-shaped mesogen(cyanobutylbiphenyl) showing characteristic amphiphilic features of hydrophobic andhydrophilic regions on either side of a rigid core, (B) disc-shaped (discotic) mesogen,and (C) bent-core (banana-shaped) mesogen [12].Kevin J. Bigham, PhD. 2016; this revision 2018 Zeus Industrial Products, Inc.5
LCP Introduction To Liquid Crystal Polymers ABCFigure 5: Selected liquid crystal structure types: (A) Rod-like mesogen (4-methoxycinnamic acid) in nematic crystal,(B) discotic mesogen in a columnar crystal structure, and (C) bent-core (banana-shaped) mesogen in nematic crystallineform.LIQUID CRYSTAL POLYMERSThe liquid crystals described heretofore represent thefirst generation of discovery and subsequent study of theseunique molecules for utilitarian purposes. Later,investigators realized that liquid crystals also formed frommore complex polymeric molecules. Rather than from justsmall-molecule individual mesogens, liquid crystalpolymers (LCPs) consist of repeated monomer units butwhich are linked to form extended chain-like molecules.The primary units of the polymeric chain are attached toone another via a flexible linker which can be of varyinglengths (Fig. 6). These polymeric chains aggregate to formLCPs just as single mesogen molecules do to form liquidcrystals. The extended chain length of the polymeric units,however, affects enhanced intermolecular interactionsKevin J. Bigham, PhD.between the polymeric chains and thus has profoundeffects upon LCP behavior distinct from simple (nonpolymeric) liquid crystals.Figure 6: Representative LCP monomer. Structuralfeatures of an LCP monomer typically includehydrophobic (non-polar) and hydrophilic (polar) regionsand a flexible linker region in addition to the mesogen [13]. 2016; this revision 2018 Zeus Industrial Products, Inc.6
LCP Introduction To Liquid Crystal Polymers BIOLOGICAL LIQUID CRYSTALPOLYMERSAs suggested by Heintz and others, LCPs also exist inthe biological realm, and these molecules bear manysimilarities with their non-biological counterparts.Biological LCPs are typically of a lyotropic nature but arelikewise affected by temperature. Biological LCPmonomers, too, are amphiphilic possessing a polar groupat one end and a non-polar group at the other. Fatty acids,Afor example, possess both a hydrophobic tail andhydrophilic head and aggregate into micelles which formliquid crystals [14] (Fig. 7). More complex amphiphiliclipid molecules, the primary component of cellmembranes, and some viruses also possess liquid crystalphases [6]. DNA – the most important biological molecule– also has a liquid crystal state [15]. Each of these naturallyoccurring molecules has architectural or structural ordersthat are retained in their viscous state. Thus, despite theirlate arrival upon the scientific discovery frontier, LCPs arenot nearly as uncommon as once believed.BCFigure 7: Biological liquid crystals. (A) Amphiphilic fatty acid moleculeshowing polar head group and non-polar tail. (B) Cross-section of micellestructure formed by aggregates of fatty acid molecules. (C) Micelle liquidcrystal rod.THERMOPLASTICS AND SYNTHETICLIQUID CRYSTAL POLYMERSThe liquid crystal polymers generating much interesttoday are particularly those in the area of thermoplastics.Thermoplastic polymers, including LCPs, exist ineveryday use and are known by such familiar names ylene (PP), polytetrafluoroethylene (PTFE),polystyrene (PS), and Kevlar (Fig. 8). As thermoplasticKevin J. Bigham, PhD.polymers, these materials become softer upon heating andcan be remolded to form different shapes. Whilethermoplastics are made from a variety of polymers, not allare made from liquid crystal polymers. Typical plasticpolymer chains maintain varying degrees of interactionbetween their chains when flowing, but LCPs distinguishthemselves from these because LCPs retain significantcrystallinity in their flow state. This partial crystallinestructure also imparts properties that are unique to LCPs,and these properties can be manipulated to suit a broad 2016; this revision 2018 Zeus Industrial Products, Inc.7
LCP Introduction To Liquid Crystal Polymers spectrum of applications. Since their initial development,innovations in LCP processing have produced plastics withexceptional strength, toughness, and high temperature andchemical resistance. Today, LCP plastics are employed indiverse areas ranging from laser beam deflectors toautomotive and aerospace parts to food containers.A) Polyethylene (PE)B) Polyvinyl chloride (PVC)C) Polypropylene (PP)D) Polytetrafluoro-ethylene(PTFE)E) PolymethylacrylateF) Polystyrene (PS)Figure 8: Representative thermoplastic polymer monomers. Of these, polystyrene is themost frequently incorporated into an LCP.LCP thermoplastics specifically encompass a broadgroup of organic molecules primarily based uponpolyesters and other aromatic polymers such aspolystyrene. These polymers form a range of higher orderstructures beyond those of ordinary liquid crystals ortypical polymer plastics. LCP structures are describedbased upon their connectivity and linkages. Like biologicalliquid crystal polymers, synthetic LCP structures containrepeated monomers in chains linked in a variety of waysbut which form regular repeated structures. They typicallycontain a flexible central chain connecting the more rigidmesogen segments. When not joined within the main chainof the polymer, the mesogens are usually connected to themain chain via a flexible linker segment (Fig. 9). Each LCPunit thus features the characteristic amphiphilic polar andnon-polar segments of the mesogen in addition to linkerand non-mesogen chain components.Kevin J. Bigham, PhD.Figure 9: Illustrative example of a side-chain liquidcrystal polymer. LCPs typically have three principalcomponents: a long chain-like central backbone, a flexiblelinker connecting main chain monomers and side chains,and a mesogen. This example shows an ethyleneiminemonomer main chain with the aromatic cyanobiphenylmesogens attached as side-chain pendants via a flexiblelinker in an end-on fashion.LCP chains can have varying linkages as well asvarying monomer components. Main chain LCPs havemesogenic units connected in the central or primarymolecular chain (Fig. 10A and B) [10]. LCPs can be 2016; this revision 2018 Zeus Industrial Products, Inc.8
LCP Introduction To Liquid Crystal Polymers copolymers incorporating two or more different monomers(Fig. 10B). Side chain LCPs have their mesogenic unitsconnected to the central chain or backbone as side pendants(Fig. 10C and D) [10]. LCPs may have mesogenic unitsconnected both as side chains and as part of the backbone(Fig. 10E) [10]. The manner of attachment of side groupsto the main chain or backbone of the polymer also affectstheir functionality. These groups may be joined to the mainchain via a lateral or side-on attachment, an end-on orterminal attachment, or via an off-center or shoulderattachment (Fig. 9, 10C, and D) [10]. LCP chains may alsobe crosslinked to one another forming networks that aid inpreserving the liquid crystal itself (Fig. 11) [6]. These nonlinear linkages and crosslinking likewise influence thefinal properties of the LCP [4].A) main chain LC polymerB) main chain copolymer with 1:1 ratio oftwo different monomersC) side chain end-on LC polymerD) side chain side-on LC polymerE) combined LC polymerFigure 10: Liquid crystal polymer chain types. Mesogen units are depictedas solid ovals or circles. (A) Mesogen units connected forming the main chainof the polymer. (B) Copolymer comprised of two different monomers joined ina 1:1 ratio. (C) Mesogen units connected as side pendants on the main chain inan end-on manner. (D) Mesogen units connected as side pendants in a side-onmanner. (E) Combined branched polymer with mesogens connected within themain chain and as end-on side chain attachments.ABCFigure 11: Polymer types. (A) linear, (B) branched, and (C) crosslinked.Kevin J. Bigham, PhD. 2016; this revision 2018 Zeus Industrial Products, Inc.9
LCP Introduction To Liquid Crystal Polymers COMMERCIALIZATION OF LCPs ANDTHERMOPLASTICSThe multivariate linkage and connectivitypossibilities of these polymers lend themselves to widedegrees of nuanced manipulation and synthesis. Thus, itis not surprising that LCPs have found favor in industryto bring out desired properties. Traits of polyesterplastics such as elasticity, strength, hydrophobicity,shrinkage, flame resistance, and liquid crystallinity canbe controlled through tailored synthesis methodsincluding the incorporation of other monomers to createcopolymers [16]. The resulting polymer structure thusgoverns the manner of crystalline formation and theproperties stemming from the crystal and polymer.Furthermore, the incomplete crystalline nature of LCPswhich results in their unique dual melting pointsprovides a distinctive processing window during theirflow state for manufacturing. These elements areparticularly important in the commercialization ofLCPs.For manufacturability, nearly all commerciallyprocessed LCPs incorporate p-hydroxybenzoic acid(p-HBA) as one of its monomers (Fig. 13) [17]. Thepolymers are typically derived from variouscondensation methods incorporating p-HBA andstructurally similar monomers [18]. Homopolymerscontaining only p-HBA [poly(p-hydroxybenzoic acid)]form liquid crystals which do not flow at temperaturesbelow 500 C [17]. This processing temperature,however, can be significantly reduced through theintroduction of other monomers such as bisphenol (BP),hydroquinone (HQ), terephthalic acid (TA),2,6-naphthalenedicarboxylic acid (NDA), 6-hydroxy-2naphthoic acid (HNA), isophthalic acid (IA), and others(Fig. 12) [17]. As an example, poly(4-hydroxybenzoicacid) – a high-melt polyester – is a polymer formed fromthe condensation of p-HBA monomers, whilepolybisphenol-A-teraphthatlate is produced fromterephthalic acid (TA) and bisphenol A (BP), andpoly(4-hydroxy benzoic acid-co-ethylene terephthalate)is a copolymer resulting from the condensation ofp-HBA and 4-[(2-hydroxyethoxy)carbonyl]benzoicacid (Fig. 13). Indeed, LCPs are very amenable to blendprocessing with polycarbonate, polyolefins, or otherpolyester building blocks [16].A) Bisphenol (BP)B) Hydroquinone (HQ)C) Terephthalic acid (TA)D) 2,6-naphthalene-dicarboxylicacid (NDA)E) 6-hydroxynaphthoic acid(HNA)F) Isophthalic acid (IA)Figure 12: Common additives which can be combined with p-HBA for LCP synthesis andprocessing.Kevin J. Bigham, PhD. 2016; this revision 2018 Zeus Industrial Products, Inc.10
LCP Introduction To Liquid Crystal Polymers ABCFigure 13: Example polyarylate polymer condensation reactions. (A) Polymerization of p-HBA monomers yieldpoly(p-hydroxybenzoic acid) polymer, (B) Teraphthalic acid (TA) and bisphenol A monomers yield polybisphenolA-teraphthatlate polymer (monomeric unit shown), and (C) p-HBA and 4-[(2-hydroxyethoxy)-carbonyl]benzoicacid yield poly(4-hydroxy benzoic acid-co-ethylene terephthalate). A, B, and C are polyesters as denoted by theester linkages (R′–CO–O–R″). Polybisphenol-A-teraphthatlate is the most common polyarylate.Besides the small molecule additives described above,other components, or fillers, can be added to the LCP resinto impart preferrable traits. For example, addition ofgraphite confers resistance to chemicals and wear; carbonfiber and fiberglass add strength and rigidity; carbon blackenhances electrical dissapation [16, 19, 20]; and pigmentsallow for different colors of the end product. Theseadditions to the LCP resin provide another means toimprove or otherwise alter performance of the LCPproduct and facilitate processing. This ability to vary LCPcomposition increases their range of properties andpotential applications.hydroxy-2-naphthoic acid) (Fig. 14). This copolymerpolyester is comprised of high-continuity chains and formsa random melt-processable (thermotropic) material [19].The LCP is formed in its melt phase typically attemperatures in the range of 220 C to 280 C and isextruded as a monofilament [16, 19].ZEUS LCP MONOFILAMENTIn light of the many distinct and desirable qualitiesachievable with LCPs, Zeus Industrial Products, Inc., hasdeveloped an LCP monofilament fiber with potentiallybroad applications. Zeus’ LCP monofilament is made froma proprietary method subsequent to the condensation ofp-HBA and 6-hydroxy-2-naphthoic acid (HNA). The resultof the condensation is poly(4-hydroxybenzoic acid-co-6Kevin J. Bigham, PhD.Figure 14: LCP (bottom) condensation synthesis fromp-hydroxybenzoic acid (top left) and 6-hydroxy-2naphthoic acid (top right). 2016; this revision 2018 Zeus Industrial Products, Inc.11
LCP Introduction To Liquid Crystal Polymers Structurally, the Zeus LCP monofilament fiber iscomprised of rod-like mesogenic molecules. Thesemolecules self-align during processing to form nematicliquid crystals. During processing and extrusion, themolecules become longitudinally arranged in the flowdirection resulting in enhanced strengthening of thematerial (Fig. 15) [21]. In addition to their high chaincontinuity, there is a high degree of similarity between theliquid crystal and solid-state structures of these two phasesof the LCP. The result is an LCP product with exceptionalmechanical and physical properties [16].Figure 15: Extrusion process and LCP alignment.During extrusion, polymer chains become aligned in theextrusion direction while maintaining liquid crystallineregions. The result of extrusion is increased strength ofthe LCP monofilament fiber. (Adapted from [22]).MRI-COMPATIBLE CATHETERS ANDLCP MONOFILAMENTZeus′ LCP monofilament is high grade advancedpolymer fiber that presents many preferable andKevin J. Bigham, PhD.advantageous traits for use in catheter construction formedical applications. In recent years, elimination of metalsin catheter construction has become a point of emphasis toenable catheterization during magnetic resonance imaging(MRI) medical procedures [23, 24]; these proceduresgenerally preclude the use of metal components. As thenorm, catheters are constructed over a mandrel in fourlayers: a thin-walled chemically etched liner (usuallyPTFE), braiding reinforcement, jacketing material (such asPebax or nylon), all of which are covered by a layer ofheat shrink (such as Zeus FluoroPEELZ ) (Fig. 16). Theheat shrink is applied to reflow the underlying jacketinginto the braid and bond the jacket to the etched PTFE. Thisbonding secures the jacketing, braiding, and PTFE liner tocomplete the construction, and the heat shrink is thenremoved. Historically, catheter braiding reinforcement hasbeen made of metal such as stainless steel wire because ofits strength. The finished catheter should possesssignificant strength and rigidity for pushability yet besufficiently flexible to navigate the human vasculature.Catheterization procedures requiring soft tissue detailedstructural visualization using these devices, however, usex-ray and thus expose patients and clinicians to ionizingradiation. To address this co
The orientation of the mesogen molecules lies at the heart of liquid crystal functionality. Recall that the liquid crystal lies in between the two fundamental states of liquid and solid. In a liquid, the mesogenic molecules become arbitrarily oriented with no directionality and form an isotropic fluid (Fig. 2A) [5]. These liquid state molecules
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emulsifiers will gradually increase, which will lead to the breakdown of the emulsion particles, and turn the liquid crystal structure with orderly distribution at oil-water interface into lamellar liquid crystal structure [8,9]. The photos (Figure 3) confirm that the liquid crystal structure . of emulsion changes upon rubbing, while the liquid
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