Glass Transition Temperature Of PS Research Articles

Preparation, characterization and thermal properties of the PS+Si based polymer nanocomposites

Polymer nanocomposites based on polystyrene and polycrystalline Si nanoparticles have been successfully synthesized using the solution-casting method. The scanning electron microscope and x-ray diffraction methods show that the Si nanoparticle size in the obtained nanocomposite was up to 50 nm. The thermostability of the obtained nanocomposite was studied depending on the concentration of Si nanoparticles in the PS matrix. It was found that Si nanoparticles that are distributed homogeneously in the polymer matrix act as a thermal barrier. By adding 3% Si nanoparticles into polystyrene polymer, the thermal degradation temperature of PS increases by 20°, and the decomposition rate reduces from −42,460 mg/min to −35,099 mg/min. In addition, it was shown that Si nanoparticles do not affect the PS glass transition temperature, which explains that the porous Si does not reduce the free volume for the polymer molecules to move. The polymer macromolecules just are adsorbed on the porous silicon surface, which partially limits their mobility.

An effective method of processing immiscible polymer blends into strong fiber

A unique methodology employing a “nearly co‐continuous morphology” for processing immiscible polymers into strong fiber is presented, and an immiscible polypropylene/polystyrene (PP/PS) blend is used as a model system to demonstrate the effectiveness of this methodology. The “nearly co‐continuous morphology” is easier to obtain than the fully co‐continuous structure, and yet, it provides an engineering solution to the production of strong fiber from an immiscible polymer blend. In addition, a process different from traditional melt spinning is used to prepare fiber with good mechanical properties. Traditional melt spinning involves large jet stretch and therefore introduces large interfacial orientation but little molecular orientation in polymer blends. To address this issue, the PP/PS blend is spun with nearly zero jet stretch and after solidification undergoes hot drawing at temperature close to the glass transition temperature of PS. This process sequence imparts a large degree of molecular orientation to the PP phase and produces a strong fiber. The proposed methodology can be extended to other blend systems and provides a potential route for directly recycling commingled polymer waste without preseparation or compatibilization. POLYM. ENG. SCI., 59:2052–2061, 2019. © 2019 Society of Plastics Engineers

Phase diagrams of thermally stable, polymer‐dispersed liquid crystals: Exploring the impact of chain length and chemical structure

Polymer‐dispersed liquid crystals (PDLCs) have garnered significant interest and motivated the investigation of the phase behavior of thermally stable smectic liquid crystals (LCs) via thermally induced phase separation (TIPS). In this study, we examined a series of two, biphenyl‐based smectic LCs suitable for high temperature polymer blend processing. Phase diagrams for LC/polystyrene (PS) blends at various compositions (0–60 wt%) were constructed. Less than 15 wt% of 8B8 (1,1′‐biphenyl‐4,4′‐diyl dioctanoate) LC in PS led to good polymer miscibility, while phase separation was induced at concentrations higher than 15 wt%. The LC concentration at saturation decreased with increasing aliphatic chain length. We also investigated the chain length (C6‐C16) effect on the PS glass transition temperature (Tg) at the LC saturation point. The Tg increased with increasing chain length due to reduced plasticization. We further examined the role of chemical structure (relatively less polar ether vs. more polar ester) on the phase diagram regions and the Tg of the nonpolar PS matrix, respectively. It is anticipated that these LC/PS phase diagrams will benefit elevated temperature processing for TIPS by highlighting the role of LC chemical structure and chain length on blend morphology. POLYM. ENG. SCI., 56:388–393, 2016. © 2016 Society of Plastics Engineers

Influence of Line Tension on Spherical Colloidal Particles at Liquid-Vapor Interfaces

Atomic force microscopy (AFM) imaging of isolated submicron dodecyltrichlorosilane coated silica spheres, immobilized at the liquid polystyrene- (PS-) air interface at the PS glass transition temperature, T(g), allows for determination of the contact angle θ versus particle radius R. At T(g), all θ versus R measurements are well described by the modified Young's equation for a line tension τ = 0.93 nN. The AFM measurements are also consistent with a minimum contact angle θ(min) and minimum radius R(min), below which single isolated silica spheres cannot exist at the PS-air interface.

Local Thermomechanical Analysis of a Microphase-Separated Thin Lamellar PS-b-PEO Film

We use atomic force microscopy (AFM) and hot tip AFM (HT-AFM) to thermophysically characterize a 30 nm thick film of poly(styrene-block-ethylene oxide), PS-b-PEO, and to modify its lamellar patterns having spacing of 39 ± 3 nm. AFM tip scans of the polymer film induce either abrasive surface patterns or nanoscale ripples, which depend upon the tip force, temperature, and number of scans. The evolution of the lamellar patterns is explained by the polymer film molecular structure and mode I crack propagation in the polymer combined with the stick-and-slip behavior of the AFM tip. The HT-AFM measurements at various tip-sample temperatures and scanning speeds yield several thermophysical quantities: the PEO melting temperature of 54 ± 12 °C, the PS glass transition temperature of 54 ± 12 °C, the PS-b-PEO specific heat of 3.6 ± 2.7 J g(-1) K(-1), the PEO melting enthalpy of 111 ± 88 J g(-1), and the free energy of Helmholtz for PEO unfolding (and melting) of 10(-20) J nm(-2). These quantities are obtained for PS-b-PEO volumes of 30,000 nm(3), which correspond to 30 ag of the polymer.

Structure and molecular dynamics of multilayered polycarbonate/polystyrene films

AbstractMultilayered film polycarbonate/polystyrene (PC/PS) comprising 257 layers with total thickness 125 μm was made by coextrusion process. The nominal thickness of PC layers was 680 nm, and the nominal thickness of PS layers was 290 nm. Additionally, the control samples of PC and PS with the thickness of 125 μm were coextruded in the same way. There was reasonably good correlation between the PC and PS layers real thickness as measured by AFM and the estimated thickness determined from the processing parameters. Significant shift of glass transition temperature is observed in multilayer film: for PS component toward higher temperature while PC still being glassy and for PC toward lower temperature while PS being in rubbery phase. To investigate the amplitude and geometry of fast segmental motions, the LG‐CP NMR technique under fast magic‐angle spinning was used. 2D 13C1H LG‐CP spectra of PC, PS, and PC/PS 70/30 were recorded at various temperatures. Cross sections of aromatic carbons spectra show us the influence of PC on PS and vice versa. It gives us also the information about PS and PC segmental motion as a function of temperature: above the glass transition temperature of PS, the PC component of a multilayer film, although still being in glassy state, becomes more flexible. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Wettability Transition Induced Transformation and Entrapment of Polymer Nanostructures in Cylindrical Nanopores

We apply the concept of wettability transition to manipulate the morphology and entrapment of polymer nanostructures inside cylindrical nanopores of anodic aluminum oxide (AAO) membranes. When AAO/polystyrene (PS) hybrids, i.e., AAO/PS nanorods or AAO/PS nanotubes, are immersed into a polyethylene glycol (PEG) reservoir above the glass transition temperature of PS, a wettability transition from wetting to nonwetting of PS can be triggered due to the invasion of the more wettable PEG melt. The wettability transition enables us to develop a nondestructive method to entrap hemispherically capped nanorods inside nanopores. Moreover, we can obtain single nanorods with the desired aspect ratio by further dissolving the AAO template, in contrast to the drawbacks of nonuniformity or destructiveness from the conventional ultrasonication method. In the case of AAO/PS nanotubes, the wettability transition induced dewetting of PS nanotube walls results in the disconnection and entrapment of nonwetting PS domains (i.e., nanospheres, nanocapsules, or capped nanorods). Moreover, PEG is then washed to recover the pristine wettability of PS on the alumina surface; further annealing of the PS nanospheres inside AAO nanopores under vacuum can generate some unique nanostructures, particularly semicylindrical nanorods.

Patterning dewetting in thin polymer films by spatially directed photocrosslinking

In this report we examine the dewetting of spin-cast poly (styrene) films in a confined geometry. We designed a platform for laterally confining PS by photo-patterning crosslinks in spin-coated thin films. Heating the patterned film above the glass transition temperature of PS results in localized dewetting patterns in regions that were not crosslinked, while the crosslinked pattern serves as a rigid barrier that confines the retraction of the uncrosslinked polymer in micron-sized domains. The barriers also provide a favorable surface that the liquid PS wets onto, forming a rim at the boundary of crosslinked and uncrosslinked polymer. The resulting patterns are shown to be dependent on the irradiation and annealing time, the dimensions of the uncrosslinked region and the thickness of the film.

Novel Nanostructures from Self‐Assembly of Chiral Block Copolymers

A diblock copolymer system constituting both achiral and chiral blocks, polystyrene-block-poly(L-lactide) (PS-PLLA), was designed for the examination of chiral effects on the self-assembly of block copolymers (BCPs). A unique phase with three-dimensional hexagonally packed PLLA helices in PS matrix, a helical phase (H*), can be obtained from the self-assembly of PS-rich PS-PLLA with volume fraction of PLLA f PLLAv = 0.34, whereas no such phase was found in racemic polystyrene-block-poly(D.L-lactide) (PS-PLA) BCPs. Moreover, various interesting crystalline PS-PLLA nanostructures can be obtained by controlling the crystallization temperature of PLLA (T(c,PLLA) ), leading to the formation of crystalline helices (PLLA crystallization directed by helical confined microdomain) and crystalline cylinders (phase transformation of helical nanostructure dictated by crystallization) when T(c,PLLA) < T(g,PS) (the glass transition temperature of PS) and T(c,PLLA) ≧ T(g,PS) , respectively. As a result, a spring-like behavior of the helical nanostructure can be driven by crystallization so as to dictate the transformation (i.e., stretching) of helices and to result in crystalline cylinders. For PS-PLLA with PLLA-rich fraction (f PLLAv = 0.65), another unique phase, a hexagonally packed core-shell cylinder phase with helical sense (CS*), in which the PS microdomains appear as shells and PLLA microdomains appear as matrix and cores, can be found in the self-assembly of PLLA-rich PS-PLLA BCPs. The formation of those novel phases: helix and core-shell cylinder is attributed to the chiral effect on the self-assembly of BCPs, so we named this PS-PLLA BCP as chiral BCP (BCP*). For potential applications of those materials, the spring-like behavior with thermal reversibility might provide a method for the design of switchable nanodevices, such as nanoscale actuators. In addition, the PLLA blocks can be hydrolyzed. After hydrolysis, helical nanoporous PS bulk and PS tubular texture can be obtained and used as templates for the formation of nanocomposites.

A Spring‐Like Behavior of Chiral Block Copolymer with Helical Nanostructure Driven by Crystallization

AbstractThe crystallization of helical nanostructure resulting from the self‐assembly of a chiral diblock copolymer, poly(styrene)‐b‐poly(L‐lactide) (PS‐PLLA), is studied. Various crystalline PS‐PLLA nanostructures are obtained by controlling the crystallization temperature of PLLA (Tc,PLLA), at which crystalline helices and crystalline cylinders occur while Tc,PLLA &lt; Tg,PS (the glass transition temperature of PS) and Tc,PLLA ≥ Tg,PS, respectively. As evidenced by selected‐area electron diffraction and two‐dimensional X‐ray diffraction results, the PLLA crystallites under confinement reveal a unique anisotropic character regardless of the crystallization temperature. On the basis of observed uniaxial scattering results the PLLA crystallites grown within the microdomains are identified as crystals with preferential growth directions either along the [100] or along the [110]‐axes of the PLLA crystalline unit cell, at which the molecular chains and the growth direction are normal and parallel to the central axes of helices, respectively. The formation of this exclusive crystalline growth is attributed to the spatial confinement effect for crystallization. While Tc,PLLA &lt; Tg,PS, owing to the directed crystallization by helical confinement, the preferential crystalline growth leads to the crystallization following a helical track with growth direction parallel to the central axes of helices through a twisting mechanism. Consequently, winding crystals with specific crystallographic orientation within the helical microdomains can be found. By contrast, while Tc,PLLA ≥ Tg,PS, the preferential growth may modulate the curvature of microdomains by shifting the molecular chains to access the fast path for crystalline growth due to the increase in chain mobility. As a result, a spring‐like behavior of the helical nanostructure can be driven by crystallization so as to dictate the transformation of helices, resulting in crystalline cylinders that might be applicable to the design of switchable large‐strain actuators.

Lamella reorientation in thin films of a symmetric poly(l-lactic acid)-block-polystyrene upon crystallization at different temperatures

The thin films of a symmetric crystalline-coil diblock copolymer of poly(l-lactic acid) and polystyrene (PLLA-b-PS) formed lamellae parallel to the substrate surface in melt. When annealed at temperatures well above the glass transition temperature of PLLA block (TgPLLA), the PLLA chains started to crystallize, leading to reorientation of lamellae. Such reorientation behavior exhibited dependence on the correlation between the crystallization temperature (Tc), the glass transition temperature of PS (TgPS), the peak melting point of PLLA crystals (TmPLLA), and the end melting point of PLLA crystals (Tm,endPLLA). When annealed at (Tc=) 80°C (Tc<TgPS<TODT, order–disorder transition temperature), 123°C (TgPS<Tc<TmPLLA<TODT), 165°C (TgPS<TmPLLA<Tc<Tm,endPLLA<TODT), the parallel lamellae became perpendicular to the substrate surface, exclusively starting at the edge of surface relief patterns. Meanwhile, the corresponding lamellar spacing was significantly enhanced. The PLLA crystallization between PS layers was hypothesized to account for the lamella reorientation during annealing. The crystallization, chain conformation, and possible chain folding mechanisms were discussed, based on detailed analysis of the lamellar structure before and after crystallization.

Direct Imaging of Nanoscopic Plastic Deformation below Bulk Tg and Chain Stretching in Temperature-Responsive Block Copolymer Hydrogels by Cryo-TEM

This work describes the thermoresponsive transition in polystyrene-block-poly(N-isopropylacrylamide)-block-polystyrene (PS-block-PNIPAM-block-PS) triblock copolymer hydrogels, as observed by both direct and reciprocal space in-situ characterization. The hydrogel morphology was studied in both the dry and wet state, at temperatures below and beyond the coil−globule transition of PNIPAM, using vitrified ice cryo-transmission electron microscopy (cryo-TEM), in-situ freeze-drying technique, and small-angle X-ray scattering (SAXS). The selected PS-block-PNIPAM-block-PS triblock copolymers were intentionally designed in such a molecular architecture to self-assemble into spherical and bicontinuous morphology with the poly(N-isopropylacrylamide) forming the continuous matrix. The phase behavior in bulk was directly investigated by SAXS as a function of temperature, while free-standing polymer thin films of samples quenched from different temperatures, allowed observing by cryo-TEM the changes in hydrogel microstructure. Finally, sublimation of water via controlled freeze-drying in the TEM column allowed studying systems without the presence of vitrified water, which enables direct imaging of the densely connected physically cross-linked polymer network. By combining these techniques on samples exhibiting both spherical and gyroidal morphologies, it was demonstrated that (i) PNIPAM form physically connected networks in spherical structures and bicontinuous morphologies in the gyroidal phase, (ii) in PNIPAM chains strands are strongly stretched above the polymer coil-to-globule transition, and (iii) surprisingly, upon the gel swelling process, the PS domains undergo extensive plastic deformation although temperature is always maintained well below the PS glass transition bulk temperature. The possible physical mechanisms responsible for this plastic deformation can be understood in terms of the dependence of PS glass transition temperature on the size of nanometer-scaled domains.

Molecular Motion in Surfactant Layers Inside Polymer Composites with Synthetical Magadiite

AbstractClays used in polymer‐layered silicate nanocomposites are heterogeneous. To improve insight into structure and dynamics of the interface, the iron‐free and structurally homogeneous layered silicate magadiite was synthesized. Morphology of the magadiite and the extent of intercalation in melt‐prepared composites were characterized by SEM and WAXS. Carbonyl groups in the main chain of the polymer appear to facilitate intercalation. Surfactant motion was studied by 2H NMR and CW EPR. Nanocomposite formation with PCL enhances and microcomposite formation with PS diminishes motion. The activation energies change at the glass transition temperature of PS and the melting temperature of PCL.magnified image

On the Crucial Role of Wetting in the Preparation of Conductive Polystyrene−Carbon Nanotube Composites

Polystyrene-single-wall carbon nanotube (PS-SWNT) nanocomposites were prepared by directly mixing aqueous suspensions of exfoliated SWNTs and PS latex particles. After freeze-drying and compression molding, homogeneous polymer films were obtained with well-dispersed carbon nanotubes, as evidenced by scanning electron microscopy imaging. The nanocomposite films display a low percolation threshold and high levels of electrical conductivity. Simultaneously, a considerable increase in the glass-transition temperature of PS is achieved, provided that a sufficient amount of low-molar-mass PS is present in the matrix material. It is suggested that a certain extent of molar mass segregation occurs in the samples, with shorter PS chains preferentially adsorbed onto the nanotube surface. The latter wetting mechanism is indispensable for obtaining favorable electrical and thermal properties.

Early Stage Interplay of Microphase Separation and Crystallization in Crystalline−Coil Poly(l-lactic acid)-block-polystyrene Thin Films

The interplay of microphase separation and crystallization has been investigated at the early stage of annealing the amorphous thin films of the crystalline−coil poly(l-lactic acid)-block-polystyrene (PLLA-b-PS) diblock copolymer. The homogeneous and heterogeneous films were annealed at the temperatures between the glass transition temperature of PS (TgPS) and the melting point of PLLA (TmPLLA) so that the microphase separation and crystallization were simultaneously possible. (1) The homogeneous films formed spinodal-like pattern, with the amplitude amplified to the lamellar spacing (L0), indicating the microphase separation and perpendicular orientation of the copolymer chains with respect to the surface and substrate. Afterward, abnormal relief structures (domain II, ∼30 nm in height) started and grew laterally within the original relief patterns (domain I). The surface wavevector q decayed with the time t as q ∼ t -1/3, while the growth of domain II could be described by the Avrami equation with the e...

Crystallization-Induced Undulated Morphology in Polystyrene-b-Poly(l-lactide) Block Copolymer

The crystallization of the PLLA block within the microphase-separated lamellar microdomain in a poly(styrene)-b-poly(l-lactide) (PS-PLLA) diblock copolymer was carried out from hard confinement (i.e., the crystallization temperature of PLLA (Tc,PLLA) < the glass transition temperature of PS (Tg,PS)) to soft confinement (i.e., Tc,PLLA ≥ Tg,PS), where interesting morphological evolution was observed. At Tc,PLLA < Tg,PS, a typical confined morphology was obtained, while at Tc,PLLA ≥ Tg,PS, a unique undulated morphology was seen for the first time. The amplitude and periodicity of the undulation instability are dependent upon the orientation of microphase-separated lamellae. The PLLA crystals under confinement formed perpendicular morphology having crystalline chains normal to the lamellae as evidenced by 2D small-angle X-ray scattering and wide-angle X-ray scattering. On the basis of morphological observations and crystallization kinetics studies, the undulation instability can be attributed to the change of...

Polymer film dynamics using X-ray photon correlation spectroscopy

A new method of X-ray photon correlation spectroscopy (XPCS) is applied for probing the dynamics of surface height fluctuations as a function of lateral length scale in supported polymer films. The short wavelength and slow time scales characteristic of XPCS extend the phase space accessible to scattering studies beyond some restrictions by light and neutron. Measurements were carried out on polystyrene films of thicknesses ranging from 84 to 333 nm at temperatures above the PS glass transition temperature. We present the experimental verification of the theoretical predictions for the thickness, wave vector and temperature dependence of the capillary wave relaxation times for supported polymeric films above the glass transition temperature.

Infrared-Visible Sum Frequency Generation Spectroscopic Study of Molecular Orientation at Polystyrene/Comb-Polymer Interfaces

Surface-sensitive infrared-visible sum frequency generation spectroscopy (SFG) in total internal reflection geometry has been used to study the structure of poly(vinyl n-octadecyl carbamate-co-vinyl acetate) (PVNODC) or poly(octadecyl acrylate) (PA-18) in contact with a deuterated or hydrogenated polystyrene (dPS or hPS) layer. SFG spectra from the PVNODC (or PA-18)/hPS interface show methyl and methylene peaks corresponding to PVNODC (or PA-18) and phenyl peaks corresponding to the PS. Analysis suggests that the methyl groups are tilted at angles less than 30 degrees with respect to the surface normal. The presence of a strong methylene peak suggests the PVNODC alkyl side chains contain more gauche defects at the PS/PVNODC interface in comparison to PVNODC (or PA-18)/air interfaces. On heating, the SFG intensity from the PS/PA-18 interface drops sharply near the bulk melting temperature (T(m)) of PA-18. Interestingly, a similar drop in SFG signal is also observed for the PS phenyl groups. This demonstrates the ability of the phenyl group at the PS/PA-18 interface to rearrange itself upon the solid-to-liquid transition of the PA-18 alkyl side chain, at a temperature well below the bulk PS glass transition temperature. For PS/PVNODC interfaces, the drop in SFG intensity is gradual and in agreement with the three broad transitions of PVNODC observed in the bulk.

Surface morphology of PS–PDMS diblock copolymer films

Spin coated thin films (∼400 Å) of poly(styrene)–poly(dimethylsiloxane) (PS–PDMS) diblock copolymers have been investigated using X-ray Photoelectron Spectroscopy and Atomic Force Microscopy. Surface segregation of the poly(dimethylsiloxane) blocks was studied for five diblock copolymers which ranged in molecular weight from 7 kg/mol to 500 kg/mol. The films were annealed above and below the highest glass transition temperature of the two polymer blocks but below the order–disorder transition temperature. Information concerning the chemical in-depth distribution of the films was extracted by use of peak shape analysis of the X-ray Photoelectron Spectra via the Tougaard Method. The amount of dimethylsiloxane in the uppermost part of the films was quantified as a function of annealing time and temperature. For annealing above the PS glass transition temperature, surface segregation of the dimethylsiloxane chain-ends occurs for all the studied PS–PDMS diblock copolymers. At room temperature, surface segregation takes place only when the amount of dimethylsiloxane in the diblock copolymers is small.

Extensional and shear rheometry of oriented triblock copolymers

The effects of extensional flow orientation on the rheological properties of two poly(styrene)-poly(ethylene-co-butylene)-poly (styrene) (PS-PEB-PS) triblock copolymers containing either spherical or cylindrical PS microdomains were studied by oscillatory shear and oscillatory extensional experiments. Extensional measurements revealed that below the PS block glass transition temperature pre-oriented triblocks display highly anisotropic mechanical properties. For both polymers, the storage modulus E ′ is higher along the flow direction. Above the PS glass transition temperature the materials are no longer anisotropic and the same storage moduli are obtained along the flow direction and perpendicular to it. Above the PS glass transition temperature the rheological behaviour parallel and perpendicular to the flow direction was also probed in pre-oriented and non-oriented samples by oscillatory shear rheometry. At high frequencies, the mechanical response of the triblocks was found to be independent of the orientation for both copolymers while at low frequencies a strong effect of the flow orientation could be observed. For both polymers the value of the storage modulus was found to be lower along the flow direction that perpendicular to it. This was explained by the ability of PS blocks to relax more easily along the flow direction.