Interactions of ionic surfactants with gelatin in fluid solutions and the gel state studied by fluorescence techniques,potentiometry, and measurements of viscosity and gel strength

The photobehavior of pyrene (fine structure of the monomeric fluorescence band; excited state lifetimes; excimer/monomeric fluorescence intensity ratios and excited state quenching rates by oxygen) in fluid solutions of gelatin and in the gel state, both in the absence and presence of ionic surfactants, has been examined. Surfactants considered were sodium dodecylsulfate and dodecyltrimethylammonium bromide. Potentiometric measurements performed by using surfactant selective electrodes allowed for the determination of the binding capacity of the surfactants onto gelatin in the gel state. When complemented with viscosity and gel strength measurements, the sesults obtained allow for a discussion of the effects of the surfactant-gelatin interactions on microscopic properties of the solutions or gels and their relation with macroscopic properties.     

Design of polyphosphazene hydrogels with improved structural properties by use of star-shaped multithiol crosslinkers

The feasibility of using a star-shaped crosslinker to produce a hydrogel with controlled mechanical properties and degradation rates was investigated. The aqueous blends of functional polymers and crosslinkers formed a solution at low temperature and a hydrogel with desired mechanical properties at body temperature. The introduction of star-shaped crosslinkers affected the microscopic and macroscopic properties of the hydrogel. The fabricated hydrogels could be suitable for many potential biomedical applications because of their injectability, tunable mechanical properties, controlled degradation rate and gel formation under physiological conditions.     

Concentration polydispersity in polymer gels

For swollen polymer networks there is no generally accepted relation between the macroscopic osmotic properties and the scattering behaviour. Detailed information on the relationship between these properties can, however, be deduced from complementary measurements of osmotic and elastic behaviour, small angle neutron and X-ray scattering (SANS and SAXS) and quasi-elastic light scattering. We describe such an investigation in two types of networks, differing in the mechanism of cross-linking. The SANS spectra yield information on the structure, which is generated both by the dynamics of the system and by long range static constraints. The former, arising from thermodynamic concentration fluctuations, governs the macroscopic osmotic and elastic moduli of the swollen network. The static superstructure in the gel reflects local variations in the cross-link density. The resulting concentration polydispersity, <δφ²>/φ², is determined by the details of the cross-linking procedure. Its concentration dependence as a function of gel swelling can be expressed in terms of the same macroscopic osmotic and elastic variables as those that govern the thermodynamic properties of the gel.     

Local and average diffusion of nanosolutes in agarose gel: the effect of the gel/solution interface structure

Fluorescence correlation spectroscopy (FCS) has been used to study the diffusion of nanometric solutes in agarose gel, at microscopic and macroscopic scales. Agarose gel was prepared and put in contact with aqueous solution. Several factors were studied: (i) the role of gel relaxation after its preparation, (ii) the specific structure of the interfacial zone and its role on the local diffusion coefficient of solutes, and (iii) the comparison between the local diffusion coefficient and the average diffusion coefficient in the gel. Fluorescent dyes and labeled biomolecules were used to cover a size range of solutes of 1.5 to 15 nm. Their transport through the interface from the solution toward the gel was modeled by the first Fick's law based on either average diffusion coefficients or the knowledge of local diffusion coefficients in the system. Experimental results have shown that, at the liquid/gel interface, a gel layer with a thickness of 120 microm is formed with characteristics significantly different from the bulk gel. In particular, in this layer, the porosity of agarose fiber network is significantly lower than in the bulk gel. The diffusion coefficient of solutes in this layer is consequently decreased for steric reasons. Modeling of solute transport shows that, in the bulk gel, macroscopic diffusion satisfactorily follows the classical Fick's diffusion laws. For the tested solutes, the local diffusion coefficients in the bulk gel, measured at microscopic scale by FCS, were equal, within experimental errors, to the average diffusion coefficients applicable at macroscopic scales (>or=mm). This confirms that anomalous diffusion applies only to solutes with sizes close to the gel pore size and at short time (相似文献   

Investigation on the assembled structure-property correlation of supramolecular hydrogel formed from low-molecular-weight gelator

The investigation on structure-property correlation is important for understanding the gelating mechanism of supramolecular hydrogels. In this paper, a low-molecular-weight hydrogelator (termed as gelator 1) prepared from 1,2,4,5-benzene tetracarboxylic acid (BTA) and 4-hydroxy pyridine (PHP) was able to gel water effectively. The influence of environmental stimulation, such as cooling speed and ultrasonic treatment, on the structure of the assembling fibers and the macroscopic properties of the gels was investigated via multiple techniques. The results indicated that the fiber size decreased as increasing the cooling speed and the smallest fibers were obtained under ultrasonic treatment. As the fibers became smaller, the gel with higher T(gel), lower bonded water content and higher dynamic modulus was obtained. Therefore it is possible to control the gel performances via the environmental stimulation. The relationship between the assembled structure and properties is helpful for understanding the gel formation mechanism and makes the gels suitable for different applications.     

Structure of Surfaces and Interfaces of Poly(N,N-dimethylacrylamide) Hydrogels

We investigated the surface structure of hydrogels of poly(N,N-dimethylacrylamide) (PDMA) hydrogels synthesized and cross-linked simultaneously by redox free radical polymerization. We demonstrate the existence of a less cross-linked layer at the surface of the gel at least at two different length scales characterized by shear rheology and by neutron reflectivity, suggesting the existence of a gradient in cross-linking. The composition of the layer is shown to depend on the degree of hydrophobicity of the mold surface and is weaker for more hydrophobic molds. While the macroscopic tests proved the existence of a relatively thick under-cross-linked layer, we also demonstrated by neutron reflectivity that the gel surface at the submicrometric scale (500 nm) was also affected by the surface treatment of the mold. These results should have important implications for the measurement of macroscopic surface properties of these hydrogels such as friction or adhesion.     

苯丙氨酸衍生物手性凝胶的制备及其应用

手性超分子凝胶材料在传感器、人工触角、药物缓释、细胞培养等领域表现出潜在的应用前景。本文合成了一种新型的含偶氮苯官能团的D/L苯丙氨酸手性凝胶因子ALP和ADP,具有对称且完全相反的手性信号。该凝胶因子在多种有机溶剂和水混合溶剂中均可形成稳定的淡黄色凝胶,其中在DMSO和水混合溶剂中表现出最优的成凝胶性能,临界成胶浓度可达2.0mg/mL,表明该手性凝胶因子具有良好的成凝胶性能。手性凝胶可对热、光、pH等外界环境刺激产生响应,并伴有宏观上的凝胶-溶胶相互转变。手性凝胶因子自组装形成了不同螺旋纳米纤维结构,并发现L型手性纳米纤维相对于D型手性纳米纤维对细胞具有更好的粘附与增殖效果。     

Scalable Template Synthesis of Resorcinol–Formaldehyde/Graphene Oxide Composite Aerogels with Tunable Densities and Mechanical Properties

Resorcinol–formaldehyde (RF) and graphene oxide (GO) aerogels have found a variety of applications owing to their excellent properties and remarkable flexibility. However, the macroscopic and controllable synthesis of their composite gels is still a great challenge. By using GO sheets as template skeletons and metal ions (Co²⁺, Ni²⁺, or Ca²⁺) as catalysts and linkers, the first low‐temperature scalable strategy for the synthesis of a new kind of RF–GO composite gel with tunable densities and mechanical properties was developed. The aerogels can tolerate a strain as high as 80 % and quickly recover their original morphology after the compression has been released. Owing to their high compressibility, the gels might find applications in various areas, for example, as adsorbents for the removal of dye pollutants and in oil‐spill cleanup.     

不同干燥过程对超细TiO2粉体性质的影响

考察了采用不同干燥工艺制备的TiO2粉体在粒子形貌、颗粒大小与分布、晶相组成以及比表面积和孔结构等织构和结构性质方面的差异。结果表明，利用常规的干燥方法，由水凝胶脱水所得的颗粒，颗粒间严重团聚，颗粒粒径大且分布不均匀，比表面积和孔体积最小；由醇凝胶直接脱水，则可以显著提高粉体的织构性能．而采用超临界流体干燥法则可以进一步提高粉体的性能，比表面积由水凝胶的4．88m2·g－1增大到113．8m2·g－1，提高了近30倍；孔体积由0．027cm3·g－1增大到0．41cm3·g-1．大约提高了15倍；而且其能够有效地防止粒子间的团聚，较好地保持了湿凝胶的网络结构，使颗粒尺寸降低且分布均匀，可重复性好．     

Two-component dendritic gel: effect of stereochemistry on the supramolecular chiral assembly

The self-assembly of diaminododecane solubilised by four different stereoisomeric dendritic peptides to form gel-phase materials in toluene was investigated. The second generation dendritic peptides were based on D- and L-lysine building blocks, and each contained three chiral centres. By designing dendritic peptides in which the configurations of the chiral centres were modified, and applying them as gelator units, the assembly of stereoisomers could be investigated. In all cases, the self-assembly of gelator units resulted in macroscopic gelation. However, the degree of structuring was modulated by the stereoisomers employed, an effect which changed the morphology and macroscopic behavior of the self-assembled state. Enantiomeric (L,L,L or D,D,D) gelator units formed fibrous molecular assemblies, whilst the racemic gel (50 % L,L,L : 50 % D,D,D) formed a flat structure with a "woven" appearance. Gelator units based on L,D,D or D,L,L dendritic peptides also formed fibrous assemblies, but small-angle X-ray scattering indicated significant morphological differences were caused by the switch in chirality. Furthermore, the macroscopic stability of the gel was diminished when these peptides were compared with their L,L,L or D,D,D analogues. In this paper it is clearly shown that individual stereocentres, on the molecular level, are directly related to the helicity within the fibre. It is argued that the chirality controls the pattern of hydrogen bonding within the assembly, and hence determines the extent of fibre formation and the macroscopic gel strength.     

Modeling Organic Surfaces with Self-Assembled Monolayers

The interfacial properties of organic materials are of critical importance in many applications, especially the control of wettability, adhesion, tribology, and corrosion. The relationships between the microscopic structure of an organic surface and its macroscopic physical properties are, however, only poorly understood. This short review presents a model system that has the ease of preparation and the structural definition required to provide a firm understanding of interfacial phenomena. Long-chain thiols, HS(CH₂)_nX, adsorb from solution onto gold and form densely packed, oriented monolayers. By varying the terminal functional group, X, of the thiol, organic surfaces can be created having a wide range of structures and properties. More complex systems can be constructed by coadsorbing two or more thiols with different terminal functional groups or with different chain lengths onto a common gold substrate. By these techniques, controlled degrees of disorder can be introduced into model surfaces. We have used these systems to explore the relationships between the microscopic structure of the monolayers on a molecular and supramolecutar scale and their macroscopic properties. Wettability is a macroscopic interfacial property that has proven of particular interest.     

Mathematical homogenization and stochastic modeling of energy storage systems

Mathematical homogenization theory as a multiscale modeling strategy for deriving macroscopic models is gaining relevance in modeling electrochemical energy storage systems (ESSs) for its ability to capture the detailed microstructural properties of a material. Stochastic modeling, on the other hand, captures molecular fluctuations and uncertainties associated with ESSs. In this short review, modeling ESSs using both tools is presented. Integrating mathematical homogenization theory and stochastic modeling provides an effective tool for deriving macroscopic models that accurately predict various macroscopic behavior and electrochemical properties of ESSs to enable optimization and manufacturing of high performance ESSs.     

Controlled cross-linking strategy for formation of hydrogels,microgels and nanogels

Hydrogels are a kind of unique cross-linking polymeric materials with three-dimensional networks.Various efforts have been devoted to manipulate the formation of functional hydrogels in situ and enrich the production of hydrogels,microgels and nanogels with improved modulation capacity.However,these methods always fail to tune the gel properties because of the difficulty in achieving the precise control of cross-linking extents once the gel formation is initiated.Therefore,the preparation of tailor-made hydrogels remains a great challenge.Herein,we summarize a controlled cross-linking strategy towards not only fabrication of hydrogels at nano-,micro-and macro-scales,but also achievement of controlled assembly of nanoparticles into multifunctional materials in macroscopic and microscopic scales.The strategy is conducted by controllably activating and terminating the disulfide reshuffling reactions of disulfide-linked core/shell materials with selective core/shell separation using system pH or UV triggers.So it provides a facile approach to producing hydrogels,hydrogel particles and nanoparticle aggregates with tunable structures and properties,opening up the design possibility,flexibility and complexity of hydrogels,microgels/nanogels and nanoparticle aggregates from nanoscopic components to macroscopic objects.     

Insights on electrochemical properties of gel polymer electrolytes based on methylmethacrylate

This paper explains some properties of gel polymer electrolytes, which are mostly used in lithium ion batteries. An emphasis is laid on the internal structure and its influence on the mobility of ions in the substance. The ions are solvated and located randomly in the liquid base of the gel, and their movement is predominantly determined by the Stokes law for liquid electrolytes. Polymethylmethacrylate gel is used as a model substance here. This report is based on the experience of the authors and their associates.     

Integrative chemistry portfolio toward designing and tuning vanadium oxide macroscopic fibers sensing and mechanical properties

Under certain synthetic conditions vanadium oxide gels are made of nanoribbons subunits. Due to this textural specificity it is possible to align the ribbons while employing an extrusion process, generating thereby vanadium oxide macroscopic fibers. In this process V₂O₅ gel is extruded through a syringe within a PVA (1% wt) solution rotating beaker. A composite fiber can be then extracted from the beaker. These as-synthesized fibers are bearing outstanding mechanical properties (20 GPa of Young modulus) addressed with transversal flexibility that alloys macroscopic knot formation. Furthermore, they appear to be excellent alcohol sensors, enable to detect 0.1 ppm of ethanol within 16 s at 40 °C, sensitivity being associated with a good selectivity. Subsequently, we were able to tune the fibers’ sensing and mechanical properties by varying the shear rate addressed to the vanadium oxide extruded gel. In order to better appreciate the correlation between fibers’ porosity, nanoribbons subunits alignment and the addressed properties (mechanical and sensing) we tuned the porosity making the use of latex nanoparticles inclusion followed by their calcinations while varying still the imposed sheer rate during the extrusion. Finally synthesis of hybrid PANI–V₂O₅ allowed reaching enhanced tenacity 12 J g^?1, concomitant with a loss of sensitivity. We show that all the parameters involved within the mechanical and sensing performances are acting within a strong partitioning mode rather than a cooperative one. Overall, these iterative synthetic approaches demonstrate once more the importance of the correlation between structures and properties, approaches where the integrative chemistry is appearing, via its versatility, as an essential tool of chemical science to conceive rationally functional architectures bearing enhanced properties.     

Redox‐Responsive Macroscopic Gel Assembly Based on Discrete Dual Interactions

The macroscopic self‐assembly of polymeric hydrogels modified with β‐cyclodextrin (βCD gel), ferrocene (Fc gel), and styrenesulfonic acid sodium salt (SSNa gel) was investigated. Under reductive conditions, the Fc gel selectively adhered to the βCD gel through a host–guest interaction. On the other hand, the oxidized ferrocenium (Fc⁺) gel selectively adhered to the SSNa gel through an ionic interaction under oxidative conditions. The adhesion strength was estimated by a tensile test. We finally succeeded in forming an ABC‐type macroscopic assembly of all three gels through two discrete noncovalent interactions.     

Drying dissipative structures of cationic gel spheres of lightly cross-linked poly(2-vinyl pyridine) (170 ∼ 180 nm in diameter) in the deionized aqueous suspension

Drying dissipative patterns of cationic gel crystals of lightly cross-linked poly(2-vinyl pyridine) spheres (AIBA-P2VP, 170?～?180 nm in diameter) were observed on a cover glass, a watch glass, and a Petri glass dish. Convectional patterns were recognized with the naked eyes. Two kinds of the broad rings were observed at the outside edge and inner region in the macroscopic drying pattern, and their size at the inner regions first decreased and then turned to increase as gel concentration decreased. Formation of the similar-sized aggregates, i.e., hierarchical aggregation and their ordered arrays were observed. This work supported strongly the formation of the microscopic drying structures of (a) ordered rings, (b) flickering ordered spoke-lines, (c) net structure, and (d) lattice-like ordered structures of the aggregated particles. The ordering of the similar-sized aggregates of the cationic gel spheres (AIBA-P2VP) in this work is similar to that of the large cationic gel spheres of poly(2-vinyl pyridine) (385?～?400 nm in diameter) and further to that of the anionic thermosensitive gel spheres of poly(N-isopropyl acrylamide). Role of the electrical double layers around the aggregates and their interaction with the substrates during dryness are important for the ordering. The microscopic drying patterns of gel spheres were different from those of linear-type polymers and also from typical colloidal hard spheres, though the macroscopic patterns such as broad ring formation were similar to each other.     

Micro and Macro Characterization of PEO-PPO-PEO Triblocks Hydrogels

Summary: Amphiphilic poly(ethylene oxide) - poly(propylene oxide) triblock copolymers are very appealing materials for biomedical application since they can be easily injected as liquid at room temperature while they produce a gel when in the body. On the other hand, these materials no longer hold the gel state when in presence of solvent (as physiological solutions) due to the dilution of the system. To overcome these limitations Cohn and coworkers 1 have synthesized a novel thermo-responsive systems by extending the chain of the commercially available PEO-PPO copolymer named F127. The aim of this study was to evaluate the effect of the chemical modification on the macroscopic, rheological, and microscopic, transport, properties of these new materials.     

Effects of guest microparticles on the swelling behavior of polyacrylamide gels

We report the effects of guest particles on the swelling properties of bulk polyacrylamide gels. The guest particles were the spheres of poly(N‐isopropylacrylamide) gel with submicrometer diameter, which were synthesized by an emulsion‐polymerized reaction in water. Polyacrylamide gels were prepared by a free radical polymerization reaction, immobilizing the gel microparticles with different concentrations at gelation. The macroscopic swelling ratio of this hybrid gel in a cylindrical shape was measured as functions of temperature and acetone concentration. The presence of guest particles was found to strongly affect the swelling behavior in the bulk gels when the concentration of incorporated particles exceeded a threshold. The experimental results indicated that the macroscopic volume in response to the temperature change should be determined by the guest particles above the threshold. On the other hand, the hybrid gel could not evidently shrink by adding acetone when the concentration of guest particles exceeded the threshold. To make clear the distribution of guest particles in the bulk networks, the fractured surfaces of dried gels were imaged by tapping mode atomic force microscopy. The guest particles were found to aggregate in the bulk homogeneous networks to form microdomains with densely connected structure, which became larger with increasing particle concentration. The roles of bulk networks as well as guest particles on the swelling behavior of hybrid gels were qualitatively discussed on the basis of the incorporated structure of guest particles, depending on the concentration of guest particles. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1696–1704, 2005     

Molecular Springs: Integration of Complex Dynamic Architectures into Functional Devices

Molecular/supramolecular springs are artificial nanoscale objects possessing well‐defined structures and tunable physicochemical properties. Like a macroscopic spring, supramolecular springs are capable of switching their nanoscale conformation as a response to external stimuli by undergoing mechanical spring‐like motions. This dynamic action offers intriguing opportunities for engineering molecular nanomachines by translating the stimuli‐responsive nanoscopic motions into macroscopic work. These nanoscopic objects are reversible dynamic multifunctional architectures which can express a variety of novel properties and behave as adaptive nanoscopic systems. In this Minireview, we focus on the design and structure–property relationships of supramolecular springs and their (self‐)assembly as a prerequisite towards the generation of novel dynamic materials featuring controlled movements to be readily integrated into macroscopic devices for applications in sensing, robotics, and the internet of things.