The interaction between polyelectrolyte microgels of <Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide copolymers and aqueous solutions of alcian blue

The temperature influence on the behavior of microgels based on poly-N-isopropylacrylamide (PNIPA) homopolymer, N-isopropylacrylamide copolymers with sodium methacrylate (PNIPA/MANa), sodium styrenesulfonate (PNIPA/SSNa), and sodium vinylsulfonate (PNIPA/VSNa) was studied. The comparative analysis of the temperature-induced collapse of macro- and microgels was conducted. The interaction between alcian blue and PNIPA, PNIPA/SSNa, PNIPA/VSNa, and PNIPA/MANa gels was studied. The research showed that dye sorption leads to the contraction of oppositely charged microgels. The sorption effectiveness depends on the nature of the ionogenic units. The dye sorption by PNIPA/SSNa microgels is more effective than the sorption by the corresponding macrogels. The AB sorption by PNIPA/MANa microgels is less than the sorption by the corresponding macrogels and by the PNIPA/SSNa microgels. The interaction properties are connected to the structure of the crosslinked polymer chains in the microgels.     

Dual Responsive Poly(N‐vinylcaprolactam) Based Degradable Microgels for Drug Delivery

Poly(N‐vinylcaprolactam)‐based biodegradable microgels are prepared for drug delivery application via precipitation polymerization using diacetone acrylamide (DAAM) and dimethyl itaconate (IADME) as comonomers. The microgel particles are subsequently crosslinked by addition of adipic acid dihydrazide, which reacts with the ketone groups of DAAM. Itaconic acid (IA) groups are generated by the hydrolysis of IADME units inside the microgels resulting into both pH and temperature sensitive microgel particles. Volume phase transition temperature of the obtained microgels is influenced by both IA content and pH of the surrounding medium. Due to the incorporation of hydrazone linkages, the microgels show degradation under acidic conditions. These microgels can effectively encapsulate doxorubicin (DOX) as a model drug and show low DOX leakage under physiological conditions while rapid DOX release is observed at low pH. The results of the cytotoxicity assay further display that the DOX‐loaded microgels exhibit effective antitumor activity against HeLa cells demonstrating their great potential as drug delivery carriers for cancer therapy.     

Sono-respond on thermosensitive polymer microgels based on cross-linked poly(N-isopropylacrylamide-co-acrylic acid)

Ultrasound (US) exposure strongly influenced thermosensitivity of microgels attracted with both N-isopropylacrylamide (NIPAM) and acrylic acid (AA) segments, due to that hydrogen bonds of carboxylic acid segments in microgels were broken by US and then the hydration with water occurred. US induced critical effects on the volume phase transition temperature of the swelled NIPAM gel (PNAM). It was observed after the US exposure that the particle size was increased and the phase transition of the microgels shifted toward larger temperature regions of the hydrodynamic diameter. FT-IR spectroscopic data of the swelled microgel showed that the free OH stretching band intensity of the COOH segments was enhanced by the exposure, but the band intensity returned to its original level without the US exposure. This meant that the US stimulus broke hydrogen bonding of the microgel and induced hydration of water in the hydrogel environment. Finally, regeneration of the hydrogen bonds in the microgel was occurred after the US exposure.     

Reversible Gelation and Phase Transition of Aqueous Solution of Hydrophobically Modified Poly(N‐Isopropylacrylamide)

Abstract

We investigated physical gelation and phase transition of aqueous solutions of hydrophobically modified poly(N‐isopropylacrylamide) (HM‐PNIPAAm) with stearyl acrylate (SA). Aqueous solutions of HM‐PNIPAAm form a reversible gel cross‐linked with hydrophobic aggregations of stearyl groups. The physically cross‐linked HM‐PNIPAAm gel with relatively low SA content shows a two‐step volume transition with increasing temperature. Moreover, overlapping of the reversible gel–sol transition and phase separation results in the phase diagrams of the aqueous solutions of HM‐PNIPAAm, having five distinct regions: dilute sol, gel, gel–sol, sol–sol, and condensed sol regions. The overlapping of the two different phase transitions causes the two‐step volume transition.     

Steady state fluorescence technique for studying phase transitions in PAAm–PNIPA mixture

The steady state fluorescence (SSF) technique was used to study the sol-gel phase transition during free radical crosslinking copolymerisation of various amounts of acrylamide (AAm) and N-isopropylacrylamide (NIPA) mixtures. N,N′-methylenebis (acrylamide) (BIS) and ammonium persulfate (APS) were used as crosslinker and an initiator, respectively. Pyranine (8-hydroxypyrene-1, 3, 6-trisulfonic acid, trisodium salt, HPTS) was added as a fluoroprobe for monitoring the polymerisation. It was observed that pyranine molecules bind to AAm and NIPA chains upon the initiation of the polymerisation, thus the fluorescence spectra of the bonded pyranines shift to the shorter wavelengths. Fluorescence spectra from the bonded pyranines allowed us to monitor the sol-gel phase transition, without disturbing the system mechanically, and to test the universality of the sol-gel transition as a function of polymer concentration ratios. Observations around the gel point of PAAm–PNIPA mixtures show that the gel fraction exponent β obeyed the percolation result.     

Thermo-sensitive N-n-propylacrylamide gels

Thermo-sensitive gels were prepared by irradiating aqueous solutions of poly(N-n-propylacrylamide) (NNPA) and its copolymers with acrylic acid (AA) with γ-rays from a ⁶⁰Co source. The equilibrium swelling volume of the gel in water was determined as a function of temperature. NNPA gel showed a discontinuous and reversible volume phase transition. The transition temperature and the volume change at the transition decreased with irradiation time. The transition temperature was approximately 12°C lower than that of poly(N-isopropylacrylamide) gel. A discontinuous volume transition was also observed in the copolymer gels of NNPA and AA. The dependence of the transition temperature on the concentration of carboxyl groups revealed a marked difference depending on whether they were protonated or dissociated. For gels having side groups of COONa, the transition temperature rose and the volume change at the transition was elevated as the COONa concentration increased. In contrast, an increase in the COOH concentration resulted in a decrease in the transition temperature. These results are discussed in terms of an equation of state constructed based on scaling theory.     

Temperature Controlled Sequential Gelation in Composite Microgel Suspensions

Depending on the volume fraction and interparticle interactions, colloidal suspensions can exhibit a variety of physical states, ranging from fluids, crystals, and glasses to gels. For microgel particles made of thermoresponsive polymers, both parameters can be tuned using environmental parameters such as temperature and ionic strength, making them excellent systems to experimentally study state transitions in colloidal suspensions. Using a simple two‐step synthesis it is shown that the properties of composite microgels, with a fluorescent latex core and a responsive microgel shell, can be finely tuned. With this system the transitions between glass, liquid, and gel states for suspensions composed of a single species are explored. Finally, a suspension of two species of microgels is demonstrated, with different transition temperatures, gels in a sequential manner. Upon increasing temperature a distinct core–sheath structure is formed with a primary gel composed of the species with lowest transition temperature, which acts as a scaffold for the aggregation of the second species.     

分子量分布对线性PNIPA/D20溶液相变和扩散性质的影响

利用¹H NMR谱和NMR自扩散方法研究了2种不同分子量分布的聚（N-异丙基丙烯酰胺）（PNIPA）的相变行为和扩散性质,发现分子量分布对PNIPA水溶液的相变行为和扩散性质都有明显影响. 在PNIPA水溶液的相变温度-浓度曲线中,宽分子量分布PNIPA的曲线下降比较平缓,而低分子量分布PNIPA的曲线先是快速降低,然后趋于缓和. 在扩散实验中,宽分子量分布PNIPA的自扩散衰减曲线呈现一定的曲率,而且温度越低,浓度越高,曲率越大;而窄分子量分布PNIPA的自扩散衰减曲线几乎是直线,受温度和浓度的影响很小. 通过基于经典的Kohlrausch Williams-Watts延展指数关系式来拟合宽分子量分布PNIPA自扩散系数和常规方程拟合窄分子量分布PNIPA自扩散系数的2种方法对比,可以得到基于Kohlrausch-Williams-Watts的延展指数拟合,有效改善分子量分布造成的影响.     

Electrocaloric effect in antiferroelectric PbZrO3 thin films

Antiferroelectric PbZrO₃ thin films have been deposited on Pt(111)/Ti/SiO₂/Si substrate by polymer modified sol–gel route. Temperature dependent P –E hysteresis loops have been measured at 51 MV/m within a temperature range of 40 °C to 330 °C. The maximum electrocaloric effect ～0.224 × 10^–6 K mV^–1 has been observed near the dielectric phase transition temperature (235 °C) of the thin films. The electrocaloric effect and its strong temperature dependence have been attributed to nearly first‐order phase transition. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hydrostatic pressure driven spin,volume and band gap collapses in SmFeO3: a GGA + U study

The crystal structure, magnetic and electronic properties of SmFeO₃ under hydrostatic pressure have been studied by first-principles calculations within the generalized gradient approximation plus Hubbard U (GGA + U). The iso-structural phase transition with spin, volume and band gap collapses can be induced by a large enough hydrostatic pressure. The high-spin (HS) state of Fe³⁺, with the magnetic moment of ~4 μ_B, is retained at low pressure. The spin crossover occurs at a transition pressure (~68 GPa) with the magnetic moment of Fe³⁺ decreasing to ~1 μ_B in low-spin (LS) state. Meanwhile, the reductions of cell volume (by ~?5.43%) and band gap (from >2 eV to ~1.6 eV) of SmFeO₃ are obtained when the HS–LS transition happens. Finally, the critical pressure of HS–LS transition, magnetic and electronic properties are found to be Hubbard U dependent.     

Size effect in isometric PbTiO3 crystals

The phase transitions Pm3m⇄P4mm and domain-structure formation in 5–500 μm isometric PbTiO₃ crystals were investigated. The phase transition is characterized by a high rate and by the formation of a single flat interphase boundary {023}. A size effect was observed: In crystals smaller than a critical size (about 20 μm), formation of 90° domains stops and, in agreement with a phenomenological theory, the temperature hysteresis of the phase transition doubles. Fiz. Tverd. Tela (St. Petersburg) 40, 1546–1547 (August 1998)     

Kinetics analysis of volume phase transition of intelligent neutral thermo-sensitive hydrogels

In this work, utilizing the first law of thermodynamics and the Flory mean-field theory, the kinetic deformation studies concerning the volume phase transition of the neutral thermo-sensitive hydrogels were performed analytically. The hydrogel was assumed as a biphasic mixture medium in the framework of the continuum mixture theory. From the energy conservation of the thermodynamics system of the hydrogel, the governing equations for the kinetics of the nonlinear large deformation were derived. The explicit analytical expressions of the effective stress tensor and the chemical potential of the fluid of the thermo-sensitive hydrogel PNIPA were also obtained from the Helmholtz free energy, which can model the steady-static volume phase transition quantitatively.     

Diffuse phase transition in a surface quartz layer with variations in temperature

The temperature dependence of the α-phase concentration in surface layers of a solution-grown quartz crystal has been studied in the range 290–820 K. This has been achieved by measuring the intensity of the 695.1, 785.0, and 1061.5 cm^?1 bands in the ?″(ν) IR damping spectra. It has been found that, in a surface layer ～0.15 μm thick, the concentration of the α-phase behaves with increasing temperature as expected for a first-order phase transition, namely, before 800 K, it remains constant, after which at T → 846 K, tends to zero. At a distance from ～1 to 20 μm from the surface, however, the concentration of the α-phase starts to decrease already at ～350 K, while at 812 K it decreases to one-fifth of the original value. This is paralleled by an increase in the intensity of the 804 cm^?1 band assigned to the β-phase. The diffusive pattern of the α-β phase transition is initiated by distortion of the quartz crystal lattice around growth dislocations. The internal stresses arising in these layers have been estimated from the shift of the band maxima. It has been established that at distances up to ～1 μm from the surface, tensile stresses reaching ～300–400 MPa appear at 400 K. These stresses drive in the surface layer of the macrocrystal microcracks culminating in total destruction of the sample. The appearance of tensile stresses is assigned to an increase in volume of the macrocrystal layer located at a distance from ～1 to 20 μm from the surface and the growth in it of the β-phase concentration. At the same time, compressive stresses develop in a layer ～1 to 20 μm thick at a temperature above 500 K, which reach a maximum at ～650 K, to fall off thereafter with increasing temperature. The compression is caused by vibrations of growth dislocation loops in the temperature range specified.     

First-principles study on superconductivity of solid oxygen

The superconductivity of solid oxygen in ζ phase was investigated by first-principles calculations based on the density functional theory. Using a monoclinic C2/m structure, we calculated the superconducting transition temperature by the Allen–Dynes formula and obtained 2.4 K at 100 GPa for the effective screened Coulomb repulsion constant μ* of 0.13. The transition temperature slowly decreases with increasing pressure and becomes 1.3 K at 200 GPa. The phonon analysis shows that the electron–phonon coupling is dominantly enhanced by the intermolecular vibrations of O₂ rather than the intramolecular ones. The phonon modes showing the strong electron–phonon coupling were found to be concentrated in the phonon frequency range of 100–150 cm^?1 at around the M-point in the Brillouin zone.     

X-ray scattering and volumetric <Emphasis Type="Italic">P-V-T</Emphasis> studies of the dimyristoylphosphatidylcholine-water system

The results of a study of the temperature and pressure dependence of isothermal compressibility of dimyristoylphosphatidylcholine (DMPC) are presented. The data were obtained using a small-angle X-ray scattering instrument in the Institute of Synthetic Polymer Materials (Moscow, Russia) and a device designed in the Laboratory of Neutron Physics, Joint Institute for Nuclear Research (Dubna, Russia), for studying the liquid systems by a volumetric P-V-T method. The minute baric investigation of the region of the main phase transition (transition from the gel phase into the liquid crystalline phase) was carried out. The points of the main phase transition were determined, and the phase diagram of DMPC was plotted over the pressure range of 1–800 bar at temperature from 24 to 35°C.     

Mössbauer studies of Fe inclusions in synthetic diamond

Mössbauer spectroscopy has been used to study the hyperfine interaction at Fe inclusions in a suite of MDAS synthetic diamonds of grain sizes in the range 25–250 μm. For the 250 μm grains a six line spectrum typical of α-Fe is obtained. With decreasing grain size the spectra reflect a rapid phase transition of the Fe inclusions from ferromagnetic to paramagnetic. A surprising result is the re-appearance of ferromagnetic structure in the spectrum of the finest grains studied. Electric quadrupole splitting in some of the spectra suggest that a small fraction of the Fe form Fe?C bonds at substitutional sites in the diamond lattice.     

The equation of state of triolein up to 1 GPa

In this paper, the compressibility studies of triolein up to 1 GPa at temperature range from 10°C to 50°C have been presented. The discontinuity of V(p) relation, characteristic for the first-order phase transition was observed. At higher temperatures (40°C and above), the time necessary for the phase transition rises considerably. Also the pressure–volume hysteresis due to the phase formation–decomposition cycle was enlarged.     

Sonochemical preparation of high surface area MgAl2O4 spinel

High surface area MgAl(2)O(4) has been synthesised by a sonochemical method. Two kinds of precursors were used, alkoxides and nitrates/acetates and in both cases nanostructured MgAl(2)O(4) was obtained. The effect of the addition of a surfactant during the sonication, cetyl trimethyl ammonium bromide, was also investigated. In the case of alkoxides precursors the as-made product is a mixture of hydroxides of aluminium and magnesium, while with nitrates/acetates a gel is obtained after sonication, containing the metal hydroxides and ammonium nitrate. Heating at 500 degrees C transforms the as-made products into MgAl(2)O(4) spinel phase. The surface area is up to 267m(2)/g after treatment at 500 degrees C and 138m(2)/g at 800 degrees C.     

Laser Light and X-Ray Diffraction Studies of Oriented Isotactic Polypropylene (iPP) Prepared by Temperature Slope Crystallization

Isotactic polypropylene (iPP) film was melt-crystallized in a temperature gradient. The iPP film showed well oriented α- and β-crystalline textures along the gradient. The crystalline structure, phase transition boundary and lamellar twisting were examined by X-ray diffraction and laser light diffraction (LLD). On the α-β boundary, LLD shows a sharp streak perpendicular to the boundary, where the a-axis of the β-crystal is oriented perpendicular to the temperature gradient. Apart from the boundary, the a-axis of the β-crystal becomes parallel to the gradient. The β-crystal shows lamellar twisting with a pitch of 200 μm at room temperature. When heated the β-crystal, the lamellar distance of 295Å at room temperature decreases to 285Å at 80–100°C and then increases to more than 300Å above 120°C. During the heating, the value of the twist period increases from 200 to 210 μm at 90–100°C, and then to above 224 μm at 140°C. The increase of the twist period is related to the increasing crystalline thickness of the β-lamellae.