Rheological analysis of the adhesion surface with a scanning probe microscope (SPM)

The frictional forces between pressure sensitive adhesives (PSAs), including rosin tackifier resin, and a probe tip were measured with scanning probe microscopy (SPM). A peak that appeared in the scanning rate-frictional force curve shifted to a lower scanning rate with decrease in temperature. The frictional force reflects rheological behavior of the PSA. In the case of the miscible system, the tendency of a peak to shift to a lower scanning rate was observed with increase in tackifier content; however, in the case of the immiscible system, no remarkable shift was observed. The frictional force is influenced by viscoelastic properties of the PSA, which systematically changed with miscibility. The high-scanning rate resulted in the interfacial failure on the surface, while the low-scanning rate resulted in the cohesion failure.     

Miscibility and fracture energy of probe tack for acrylic pressure-sensitive adhesives: acrylic copolymer/tackifier resin systems

The relationship between the miscibility of acrylic pressure-sensitive adhesive (PSA) and the fracture energy (W) (Jm⁻²) of the probe tack was investigated, wherein the master curve of W was compared with that of the maximum force (σ_max) (gf) of the probe tack. It was ascertained that W of acrylic PSA was closely related to the miscibility between the components (acrylic copolymer and tackifier resin). In the case of the miscible blend system, the master curve of W shifted toward the lower rate side and, at the same time, the magnitude decreased as the tackifier resin content increased. The degree of the shift of W was extremely smaller than that of σ_max. In the case of the immiscible blend system, the master curve of W remarkably decreased as the tackifier resin content increased, which suggests the fact that W of the PSA depended on the dynamic mechanical properties of the matrix phase and that the resin-rich phase acted as a kind of filler, thus reducing the practical performance. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 581–587, 1998     

Miscibility and Probe Tack of Acrylic Pressure Sensitive Adhesives—Acrylic Copolymer/Tackifier Resin Systems

Miscibility between acrylic copolymers and tackifier resins are investigated in terms of phase diagrams, and the probe tack of the blends are measured as a function of both temperature and rate of separation in order to obtain the master curves. It is found that the probe tack of the pressure sensitive adhesives are closely related to the miscibility between the components. The master curves of the miscible blends shift along the X(rate)-axis according to the change of T_g of the bulk materials with a gradual variation of the peak heights. However, those of the immiscible blends will not shift along the X(rate)-axis, but the magnitude will decrease with increase of a dispersed phase.     

Miscibility and lower critical solution temperature type phase behavior of poly(ethyl acrylate)/poly(vinylidene fluoride-cohexafluoro acetone) blends

Summary The miscibility of mixtures of poly(ethyl acrylate) (PEA) with poly (vinylidene fluoride-co-hexafluoro acetone) (P(VDF-HFA)) was investigated with optical microscopy and differential scanning calorimetry (DSC). In PEA/P(VDF-HFA) blends with P(VDF-HFA) content of 50 and 70(wt%), the heterogeneous phase morphology was observed on optical micrographs at 210°C. It was found that PEA/P(VDF-HFA) blends showed the lower critical solution temperature type (LCST) phase behavior. The endothermic peak for PEA / P(VDF-HFA) blend observed on DSC thermogram near 200°C corresponded to the liquid-liquid phase transition temperature as shown in the heterogeneous phase morphology with optical microscopy. It was expected that the endothermic peak is the transition temperature from miscibility to immiscibility.     

Fabrication of Amphiphilic Hot-Melt Pressure Sensitive Adhesives for Transdermal Drug Delivery

Abstract

Styrene-isoprene-styrene (SIS) copolymer and tackifier resins can be utilized to prepare hot-melt pressure sensitive adhesives (HMPSAs) for the transdermal delivery of high lipophilic drugs. To meet the requirement of transdermal delivery of Chinese medicine (containing different ingredients including lipophilic, amphiphilic and hydrophilic drugs), amphiphilic HMPSAs were developed by melt-blending HMPSAs, poly(ethyl acrylate-co-methyl methacrylate-co-trimethylammonioethyl methacrylate chloride) (RLPO) and polyethylene glycol 2000 (PEG2000). Their morphological structures and miscibility were characterized with phase microscopy and differential scanning calorimetry. Their 180° peel strength and holding power were measured for their adhesive performances. In vitro drug release experiments were carried out using a modified Franz type horizontal diffusion cells, in which three ingredients of gardenia fruit (oleanic acid, luteolin and geniposide) were chosen as representatives of lipophilic, amphiphilic and hydrophilic drugs. It was found that amphiphilic phase structures were developed with the addition of RLPO and PEG2000. As the SIS/RLPO ratio was 1:1～1:2, the HMPSAs had miscible and amphiphilic phase structures. Drug release results showed that hydrophilic drugs could be released due to the existence of RLPO and PEG2000. Its release rate was rapidly enhanced with the increment of RLPO and PEG2000. Meanwhile, the release behavior of lipophilic and amphiphilic drugs and adhesive performance of HMPSAs were preserved in the experiment range. It was proposed that the addition of RLPO and PEG2000 did not destroy phase structures of SIS and tackifier, which insured appropriate adhesive performance and the amphiphilic polymer skeleton of SIS/RLPO/PEG2000 as release channels of various drugs.     

Development of hot-melt pressure–sensitive adhesives for transdermal drug delivery

Styrene–isoprene–styrene (SIS) copolymer was epoxidized by in situ epoxidation to prepare a series of epoxidized SIS resins (ESIS). Their epoxidation degrees, phase structures, and compatibility with hydrocarbon resin were characterized with ¹H nuclear magnetic resonance spectroscopy, atomic force microscopy, and differential scanning calorimetry, respectively. These ESIS resins were melt-mixed with synthetic hydrocarbon resin, mineral oil, and antioxidants to fabricate a series of ESIS-based hot-melt pressure–sensitive adhesives (HMPSAs), which were used as carriers of transdermal drug delivery system. Their adhesive performances were measured, including holding power and 180^o peel strength. Geniposide and oleanic acid were representatively chosen as hydrophilic and lipophilic drug, respectively. Their in vitro release behaviors in ESIS-based HMPSAs were investigated using a modified Franz-type horizontal diffusion cells. Although the introduction of epoxide groups could alter the compatibility and phase structures between SIS resins and additives, the adhesive performances were slightly affected, as SIS resins had lower epoxidation degree (<15%). It is even more important that the cumulative release rate of both hydrophilic and lipophilic drugs is markedly enhanced with the increase of epoxidation degree in these ESIS-based HMPSAs. Therefore, this kind of HMPSAs has a promising future as a carrier of transdermal drug delivery system as their SIS resins are appropriately epoxidized.     

The study of poly(styrene-co-p-(hexafluoro-2-hydroxylisopropyl)-α-methyl-styrene)/poly(propylene carbonate) blends by ESR spin probe and Raman

Different hydroxyl content poly(styrene-co-p-(hexafluoro-2-hydroxyisopropyl)-α-methylstyene) [PS(OH)] copolymers were synthesized and blends [noted for PP-X] with poly(propylene carbonate) [PPC] were prepared by casting from chloroform solution. The miscibility, micro heterogeneity and hydrogen bonding interaction of the component polymers were investigated by Differential Scanning Calorimetry (DSC), Electron Spin Resonance (ESR) spin probe method and Micro Raman spectroscopy. DSC results showed that the PP-2, PP-5, PP-8, PP-12 blends exhibited two distinct T_gs, indicating immiscibility, while the PP-20 and PP-27 blends were miscible with the existence of a single T_g. ESR results indicated that the probe molecule: Tempo couldn't give clear micro phase separation or miscibility information and thus was not sensitive to the investigated polymer blends system. On the contrary for all the blends spin probed with the probe molecules: Tempol and Tamine, two spectral components with different rates of motion: ‘fast’ and ‘slow’ motion were observed in different temperature range, which indicated the existence of micro heterogeneity on the molecular level; the more mobile PPC-rich micro phase and the more rigid PS(OH) rich micro phase. In addition, the scale of miscibility was progressively enhanced due to the increasing hydrogen bonding interaction between the hydroxyl in PS(OH) and the oxygen atoms in PPC. Meanwhile it was found that the degree of the probe molecule rotation detectable in the ESR spectrum was dependent on the polymer matrix rigidity and the strength of the hydrogen bonding between the probe molecule and the polymer matrix. Micro Raman substantiated the existence of the PS(OH)-rich micro phase and the PPC-rich micro phase. The hydrogen bonding strength between PS(OH) and PPC and the mixing level of the component polymers were increased gradually with the increase of hydroxyl content in the PS(OH) copolymer.     

Theoretical representation of shear and pressure influence on the phase separation behavior of PVME/PS mixture

In the framework of lattice fluid model, the Gibbs energy and equation of state are derived by introducing the energy (E_s) stored during flow for polymer blends under shear. From the calculation of the spinodal of poly(vinyl methyl ether) (PVME) and polystyrene (PS) mixtures, we have found the influence of E_s on equation of state in pure component is inappreciable, but it is appreciable in the mixture. However, the effect of E_s on phase separation behavior is extremely striking. In the calculation of spinodal for the PVME/PS system, a thin, long and banana miscibility gap generated by shear is seen beside the miscibility gap with lower critical solution temperature. Meanwhile, a binodal coalescence of upper and lower miscibility gaps is occurred. The three points of the three-phase equilibrium are forecasted. The shear rate dependence of cloud point temperature at a certain composition is discussed. The calculated results are acceptable compared with the experiment values obtained by Higgins et al. However, the maximum positive shift and the minimum negative shift of cloud point temperature guessed by Higgins are not obtained. Furthermore, the combining effects of pressure and shear on spinodal shift are predicted.     

Miscibility and pressure‐sensitive adhesive performances of acrylic copolymer and hydrogenated rosin systems

Relationship between the miscibility of pressure‐sensitive adhesives (PSAs) acrylic copolymer/hydrogenated rosin systems and their performance (180° peel strength, probe tack, and holding power), which was measured over a wide range of time and temperature, were investigated. The miscible range of the blend system tended to become smaller as the molecular weight of the tackifier increased. In the case of miscible blend systems, the viscoelastic properties (such as the storage modulus and the loss modulus) shifted toward higher temperature or toward lower frequency and, at the same time, the pressure‐sensitive adhesive performance shifted toward the lower rate side as the T_g of the blend increased. In the case of acrylic copolymer/hydrogenated rosin acid systems, a somewhat unusual trend was observed in the relationship among the phase diagram, T_g, and the pressure‐sensitive adhesive performance. T_g of the blend was higher than that expected from T_gs of the pure components. This trend can be due to the presence of free carboxyl group in the tackifier resin. However, the phase diagram depended on the molecular weight of the tackifier. The pressure‐sensitive adhesive performance depended on the viscoelastic properties of the bulk phase. A few systems where a single T_g could be measured, despite the fact that two phases were observed microscopically, were found. The curve of the probe tack of this system shifted toward a lower rate side as the T_g increases. However, both the curve of the peel strength and the holding power of such system did not shift along the rate axis. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 651–663, 1999     

Morphology and mechanical properties of semi-interpenetrating polymer networks from polyurethane and benzyl konjac glucomannan

A series of semi-interpenetrating polymer network (semi-IPN) films coded as UB from castor oil-based polyurethane (PU) and benzyl konjac glucomannan (B-KGM) were prepared, and they have good or certain miscibility over entire composition range. Morphology, miscibility and properties of the UB films were investigated by using scanning electron microscopy (SEM), differential scanning calorimetry, dynamic mechanical analysis, ultraviolet spectrometer, wide-angle X-ray diffraction and tensile test. The results indicated that the UB films exhibited good miscibility when B-KGM content was lower than 15 wt%, resulting in relatively high light transmittance, breaking elongation and density. With an increase of the B-KGM content from 20 to 80 wt%, a certain degree of phase separation between PU and B-KGM occurred in the UB films. The tensile strength of the films UB increased from 7 to 45 MPa with an increase of B-KGM content from 0 to 80 wt%. By extracting the B-KGM with N, N-dimethylformamide from the semi-IPN, the morphology and phase domain size of the UB films were clearly observed by SEM. A continuous phase and dual-continuous phase model describing the semi-IPN were proposed to illustrate the morphology and its transition.     

Membrane formation with presence of Lewis acid–base complexes in polymer solution

This work investigated membrane formation using Lewis acid–base complexes in a polymer solution, which consisted of poly(ether sulfone) (PES), Lewis acid–base complexes formed by N‐methyl‐2‐pyrrolidone (NMP, Lewis base), and dicarboxylic or monocarboxylic acids from a homologous series (Lewis acids). The solutions were characterized by viscosity measurements, IR spectroscopy, cloud point determination, and light transmission experiments. The membranes were characterized by scanning electron microscopy and gas permeation tests. The results indicated that the solvent–additive interaction, which is a function of their capacity to form complexes, and the acid chain length directly affect the viscosity and miscibility region. Consequently, these parameters combined with the complex dissociation influence the precipitation velocity of the polymer solutions, which will then affect the membrane transport properties. It is also pointed out that the membranes prepared by using 25 wt % PES at the same acid/NMP molar ratios and with different acids presented permeability coefficients in agreement with the binodal shift obtained in pseudoternary phase diagrams. Furthermore, when these solutions were exposed to the environment for a long period of time, the demixing onset sequence also agreed with the miscibility region for all solutions, except for the adipic acid solution because of its extremely high viscosity. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2022–2034, 2002     

Miscibility of poly (etherimide) and poly (butylene naphthalate) blends

Summary Differential scanning calorimeter (DSC), optical microscopy (OM) and scanning electron microscopy (SEM) were performed to characterize the miscibility of a blend system comprising poly (butylene naphthalate) (PBN) and poly (ether imide) (PEI). DSC scans showed there was only one single Tg for each blend and the glass transitions increase monotonously with the increase of PEI content. The glass transition temperatures of the blends fitted the Fox equation well implying that the blends exhibited fine segmental scale of mixing. No lower critical solution temperature (LCST) was observed by OM for the blends. SEM micrographs showed the fracture surface of quenched sample exhibited a homogeneous structure. No obvious IR peak shift of C=O absorption at 1780 cm⁻¹ was observed suggesting a relatively low level of specific interaction between two molecules. It was concluded that these blends were miscible with non-specific intermolecular interactions. Received: 5 January 2001/Accepted: 27 February 2001     

Probing polymer interdiffusion in carboxylated latices with force modulation atomic force microscopy

Interdiffusion of polymer chains between latex particles is a prerequisite for the development of good mechanical strength and homogeneity in a latex film. This process may be retarded in carboxylated latices if the particles are surrounded by a hard cell wall consisting of ionic groups on the particle surface. The presence of an ionic cell wall can be indirectly detected by atomic force microscopy (AFM) because surfactant migration to the film/air interface is retarded compared with a non-ionic case. In this paper we have used force modulation atomic force microscopy to directly probe the relative polymer density across the film surface during annealing thereby qualitatively monitoring the interdiffusion process. The applicability of this method to study polymer interdiffusion will be discussed.     

Dielectric and morphological investigations of phase separation and cure in rubber-modified epoxy resins: Comparison between teta- and DDM-based systems

Real-time and equilibrium dielectric measurements, covering the frequency range 10^?1–10⁵ Hz, are reported on a series of rubber-modified epoxy resins, based on reaction of the diglycidyl ether of bisphenol A (DGEBA) with either triethylenetetramine (TETA) or diaminodiphenylmethylene (DDM). The rubber modifier used was a carboxyl-terminated butadiene acrylonitrile (CTBN) reactive oligomer and the phase-separated structure, the results of which was examined using both dielectric and electron microscopic techniques. The mixture was initially homogeneous, but after a short period of time, it underwent phase separation and this process was marked by the appearance of a dielectric peak associated with ion-charge migration within the occluded rubbery phase. Analysis of the peak provided information on the morphology of the system and these data were compared with information obtained from scanning electron microscopy. A phase-separated morphology was observed consisting of spherical rubber particles dispersed in an epoxy matrix. For high concentrations of rubber ≥ 10 wt %, precipitation of epoxy domains within the rubbery phase was observed. Detailed dielectric studies of the peak associated with phase separation revealed that in the case of the TETA system the peak continued to shift after vitrification, whereas in the case of DDM, it was invariant with time. The point at which the peak appears was used to determine the time at which phase separation occurred. Differences observed in the lower temperature dielectric spectra were associated with variations in the form of the phase structure and possibly reflect different degrees of densification of the matrix. Good agreement was observed between the predictions of the Maxwell—Wagner—Sillers (MWS) theory and experimental observation for these systems. © 1993 John Wiley & Sons, Inc.     

Phase Diagram for Liquid Crystalline Polymer/ Polycarbonate Blends

A novel mechanism to form binary polymer blends is through phase separation by spinodal decomposition in the unstable region of the phase diagram. The present work investigates the effects of thermally‐induced phase separation by spinodal decomposition on the morphology development of liquid crystalline polymer/polycarbonate blends. Moreover, a thermodynamic binary phase diagram is obtained using a twin‐screw extruder at various processing melt temperatures. Differential scanning calorimetry and scanning electron microscopy were used to study the miscibility of the blends and the resulting morphology. A thermodynamic binary phase diagram exhibiting a lower critical solution temperature was obtained. The droplet size distribution of the blend was also obtained and discussed in light of the Cahn‐Hilliard theory.     

Phase distribution changes of neat unsaturated polyester resin and their effects on both thermal stability and dynamic-mechanical properties

A relationship between phase distribution of a commercial unsaturated polyester resin (UPR) and both thermal stability and dynamical mechanical properties, measured by thermogravimetric analysis and dynamic-mechanical analysis respectively, is observed. Changes in phase distributions are achieved varying UPR components miscibility by means of temperature. Morphologies of the internal surfaces are analyzed by atomic force microscopy showing that more homogeneous nanostructures with smaller nodules result in the increase of the storage modulus and glass transition temperature of the thermosetting UPR. Tan δ peaks show that the phase rich in UP and the phase rich in polystyrene tend to decrease their differences at higher curing temperatures. Changes in the curing mechanism and kinetics with curing temperature are verified by differential scanning calorimetry. A theoretical explanation of archived morphology is proposed using interaction parameter between UP and styrene showing that higher temperatures increased their miscibility.     

壳聚糖／水溶性高分子共混膜相容性的预测与表征

高分子（聚乙烯醇和聚乙二醇）间的相容性,壳聚糖与极性水溶性高分子在溶液状态时,分子间相互吸引,相容性好,向本体转化而成膜时,CS／PVA体系比CS／PEG体系有更好的本体相容性。原因可归结为PEG不能像PVA一样提供足够多的极性基团与壳聚糖分子形成强烈相互作用,CS与PEG间的氢键强度要弱于CS与PVA间的氢键;另一个方面,PEG结晶能力很强,在由溶液转化为本体而成膜过程中,PEG分子自身之间易于形成较规整的结晶而逐渐使体系发生分相。     

AFM/FTIR: A New Technique for Materials Characterization

A new type of infrared spectroscopy for obtaining the molecular composition of the surfaces of materials at ultra-high spatial resolution has been developed by combining atomic force microscopy (AFM) with Fourier-transform infrared spectroscopy (FTIR). This new analytical technique involves the use of an AFM to detect the response of a material to the absorption of modulated infrared radiation from an FTIR spectrometer and is referred to as AFM/FTIR spectroscopy. When the technique of AFM/FTIR spectroscopy is completely developed, we plan to use it to probe the molecular structure of interphases in polymer composites and adhesive bonds. Two approaches have been used to measure the response of polymer systems to infrared absorption. The first involves the use of a contact mode AFM probe to measure the thermal expansion of the polymer; the second involves using a scanning thermal microscopy (SThM) probe to measure the polymer's temperature increase. In either case, the output of the probe resembles an interferogram to which a Fourier-transform can be applied to obtain the infrared absorption spectrum. The first approach was used to obtain excellent quality AFM/FTIR spectra from various neat polymer films, including polystyrene, polycarbonate, and a model adhesive system consisting of an epoxy resin cross-linked with dicyandiamide. Excellent spectra were also obtained from polystyrene beads having a diameter of about 2 µm. The second approach, using an SThM probe to determine the temperature increase that accompanies infrared absorption, was also used to obtain interferograms of polymer samples such as polystyrene. However, the interferograms were noisy and the AFM/FTIR spectra obtained from them had a low signal-to-noise ratio. The present results, thus, show that AFM/FTIR spectroscopy is feasible but the spatial resolution of the technique remains to be shown.     

Phase behavior and density of polysulfone in binary fluid mixtures of tetrahydrofuran and carbon dioxide under high pressure: Miscibility windows

Mixtures of tetrahydrofuran (THF) and carbon dioxide (CO₂) were identified as new solvent systems for polysulfone. The miscibility and density of polysulfone in binary fluid mixtures of THF and CO₂ were investigated from 300 to 425 K at pressures up to 70 MPa. The influence of the CO₂ and polysulfone concentrations was studied, with the concentrations of the other two components kept constant. At a 4.5 wt % polymer concentration, the demixing pressures in a 10 wt % CO₂ and 90 wt % THF mixture increased with temperature (310–425 K) from 15 to 40 MPa. With increasing CO₂ concentration (from ca. 10 to 14 wt %), a significant increase (from 15 to 70 MPa at 310 K) was observed in the demixing pressures. Furthermore, with an increasing amount of CO₂, the nature of the phase boundary shifted from lower critical solution temperature behavior to upper critical solution temperature behavior. The influence of the polymer concentration was studied in the 0–5 wt % range at two CO₂ levels, with solvent compositions of 10 wt % CO₂ and 90 wt % THF and 13 wt % CO₂ and 87 wt % THF. The system with a higher level of CO₂ (13 wt %) showed highly unusual phase behavior: on pressure–composition and temperature–composition diagrams, the system displayed two distinct regions of miscibility. In the system with 10 wt % CO₂, the distinct regions of miscibility that were observed in the system with 13 wt % CO₂ partially overlapped and led to a W‐shape phase boundary. The densities of the polymer solutions were measured from the one‐phase region through the demixing point into the two‐phase region at a constant temperature. No significant change in density was found around the phase boundary; this indicated that the coexisting phases had similar densities, as is often the case with liquid–liquid phase separation in polymer solutions under high pressure. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2357–2362, 2002     

Microporous anisotropic phase inversion membranes from bisphenol A polycarbonate: Effect of additives to the polymer solution

Phase inversion is a very flexible technique to obtain membranes with a large sort of morphologies. Membrane properties can vary greatly depending on the kind of polymer system used. Bisphenol A polycarbonate (PC) could be used as a phase inversion membrane base polymer, and presents very good properties. Nevertheless, very little information on membrane preparation using PC and the phase inversion process can be found in the literature. In this work flat‐sheet microporous membranes were obtained by the phase inversion process using the immersion precipitation technique. A new polymer system was studied, consisting of polycarbonate, N‐methyl‐2‐pyrrolidone as solvent, water as the nonsolvent, and an additive. The influence of some parameters on membrane morphology, such as polymer solution composition, exposition time before immersion into the precipitation bath, and the kind of additive was investigated. Precipitation was followed using light transmission experiments and membrane morphology was observed through Scanning Electron Microscopy (SEM). The viscosity and cloud points of all polymer solutions were also determined. The results were related to the studied synthesis parameters, using the basic principles of membrane formation by the phase inversion technique, looking forward to establishing criteria to control the morphology of flat‐sheet membranes using polycarbonate as the base polymer. The results showed that both additives were able to increase pore interconnectivity and even suppress macrovoid formation. The decrease in the miscibility region of the polymer system and increase in mass transfer resistance are found to be the determining factors during polymer solution precipitation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3085–3096, 2002