Average Void Diameter Research Articles

Novel microstructured polyol–polystyrene composites for seasonal heat storage

We propose a robust route to prepare novel supercooling microstructured phase change materials (PCMs) suitable for seasonal thermal energy storage (STES) or heat protection applications. Two supercooling polyols, erythritol and xylitol, are successfully prepared as novel microencapsulated PCM-polystyrene composites with polyol mass fractions of 62wt% and 67wt%, respectively, and average void diameter of ∼50μm. Thermal properties of the composites and bulk polyols are studied thoroughly with differential scanning calorimetry (DSC) and thermal conductivity analyzer. Significant differences in heat storage properties of microstructured and bulk PCM are observed. The heat release of microstructured erythritol is more controlled than that of bulk PCM, making the novel microengineered PCMs particularly interesting for STES. In the case of bulk PCM, the heat release may occur spontaneously due to crystallization by surface roughnesses or impurities, whereas these factors have only little impact on the crystallization of microstructured erythritol, making the novel composite more reliable for long-term heat storage purposes. In addition, microstructured polyol–polystyrene composites show anomalous enhancement in the specific heat as compared to bulk polyols. This enhancement may originate from strong polyol–surfactant interactions in the composites.

Rationally designed hybrid molecularly imprinted polymer foam for highly efficient λ-cyhalothrin recognition and uptake via twice imprinting strategy

Herein we reported a novel method for preparation of hybrid molecularly imprinted polymer foams (MIPFs) via a twice imprinting strategy. Firstly, based on halloysite nanotubes (HNTs) cores, three molecularly imprinted nanomaterials (MIPs-S, MIPs-M and MIPs-L) with controlled thickness of imprinted shells (i.e., 7.0nm, 17nm and 36nm, respectively), were prepared by precipitation polymerization. The surface hydrophobicity of MIP nanomaterials gradually enhanced with the increasing thickness of imprinted shells. Secondly, three hybrid MIP foams (MIPFs-S, MIPFs-M, MIPFs-L) were successively fabricated by W/O Pickering high internal phase emulsions (HIPEs) template stabilized by the corresponding MIPs nanomaterials. Due to the increased hydrophobicity of the MIPs nanomaterials, the amount of interconnecting pores in hybrid MIPFs was continuously decreased until a closed-cell structure appeared, while the average void diameter increased from 10μm to 28μm. Binding experiments demonstrated that optimized hybrid MIP foams (MIPFs-M) possessed enhanced adsorption capacity, fast kinetics and excellent recognition ability towards λ-cyhalothrin (LC). Therefore, this two-step imprinting strategy could not only figure out the difficulty in solid–liquid phase separation and the recycling of nano-sized MIPs but also overcome the disadvantage of stabilizing solid particles on the surface of MIPFs referring to the lack of specific adsorption activity.

Effect of the entrained air void on strength and interfacial transition zone of air-entrained mortar

In order to facilitate the development and application of air entraining agents (AEA) in the high performance concrete, entrained air void structure parameters (air void size range from 10 to 1 600 μm) of 28 d sifted mortar were measured by image analysis method. The relationship between the air void size distribution and strength of mortar was studied by methods of grey connection analysis and multiple linear regression analysis. The multiple linear regression equation was established with a correlation coefficient of 0.966. The weight of the affection of hierarchical porosity on the compressive strength ratio was also obtained. In addition, the effect of air voids on the paste-aggregate interfacial transition zone (ITZ) was analyzed by microhardness. The results show that the correlation between different pore size range and the compressive strength is negative. The effect of air void size distribution on 28 days compressive strength is different: under the condition of similar total porosity, with the increase of the porosity of the air void size, ranging from 10 to 200 μm, and the decrease of the porosity, ranging from 200 to 1 600 μm, the average air void diameter and mean free spacing are decreased; as well as the width of ITZ. On the contrary, the microhardness of the ITZ is increased while the compressive strength loss is decreased.

HIPEs template: Towards the synthesis of polymeric catalysts with adjustable porous structure, acid–base strength and wettability for biomass energy conversation

Due to its widely available, inexpensive, renewable and carbon–neutral properties, biomass of cellulose is considered to be the most promising candidate to produce 5-hydroxymethylfurfural (HMF). In this work, high internal phase emulsions (HIPEs) templating methodology, subsequent ion-exchange, and the surface grafting technique are combined to synthesize macroporous, acid–base bifunctional, and superhydrophobic polymeric solid catalyst for the production of HMF from cellulose in a one-pot manner. The catalyst are well characterized by field emission scanning electron microscopy, fourier transform infrared spectroscopy, 13C solid-state nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy, pyridine fourier transform infrared spectroscopy and NH3/CO2 temperature-programmed desorption. Results of characterization demonstrated that the as-prepared catalyst possesses average void diameter at 12.5μm, interconnecting pore diameter at 2.8μm, contact angle at 150°, acid strength at 3.034mmolg−1 and base strength at 1.379mmolg−1, respectively. By simply varying the parameters of HIPEs templates (i.e., the volume fraction of the internal phase and surfactant concentration), the molar ratio between acid/base monomer and the grafted amount of 1-dodecanethiol, the pore structure, acid and base strengths, wettabilities of catalyst can be easily adjusted. Results of catalytic experiments involving cellulose-to-HMF conversion indicated that as-prepared catalyst can effectively improve the reaction rate, increase the HMF yield and prohibit the hydration of HMF to by-products. And remarkable HMF yield of 49.5% and selectivity of 55.9% can be obtained from 100mg cellulose under the optimal conditions. Furthermore, catalyst can be easily recovered and reused at least five times without significant loss of catalytic activity. This work represents a continuation of efforts for fabrication and application on multi-functional heterogeneous catalyst for excellent conversion of one-pot cellulose to HMF.

Preparation of hybrid thiol-acrylate emulsion-templated porous polymers by interfacial copolymerization of high internal phase emulsions.

Emulsion-templated highly porous polymers (polyHIPEs), containing distinct regions differing in composition, morphology, and/or properties, are prepared by the simultaneous polymerization of two high internal phase emulsions (HIPEs) contained within the same mould. The HIPEs are placed together in the mould and subjected to thiol-acrylate photopolymerization. The resulting polyHIPE material is found to contain two distinct semicircular regions, reflecting the composition of each HIPE. The original interface between the two emulsions becomes a copolymerized band between 100 and 300 μm wide, which is found to be mechanically robust. The separate polyHIPE layers are distinguished from one another by their differing average void diameter, chemical composition, and extent of contraction upon drying.

Tailoring the morphology of emulsion-based (glycidylmethacrylate-divinylbenzene) monoliths

Poly(glycidylmethacrylate-divinylbenzene) monoliths [poly(GMA-DVB)] were prepared in the presence of a porogen using a high internal phase emulsion (HIPE) template. Tripolyglycerol monostearate was used as a surfactant to effectively inhibit Ostwald ripening and coalescence, and stable HIPE containing GMA was obtained. Epoxy groups of poly(GMA-DVB) were verified by FT-IR and solid-state 13C NMR spectroscopy. The effects of surfactant amount, cross-linking degree, water fraction, and porogen amount on the surface area, average void diameter, range of void diameter, average interconnection diameter, and average pore diameter of poly(GMA-DVB) were investigated. The morphology of poly(GMA-DVB) may be tailored by tuning each of the factors described above according to the requirements of specific applications. Finally, poly(GMA-DVB) were further functionalized by diethylamine via the ring-opening reaction of epoxy groups. The results showed that most epoxy groups of poly(GMA-DVB) could react with diethylamine.

Galactose-functionalized polyHIPE scaffolds for use in routine three dimensional culture of mammalian hepatocytes.

Three-dimensional (3D) cell culture is regarded as a more physiologically relevant method of growing cells in the laboratory compared to traditional monolayer cultures. Recently, the application of polystyrene-based scaffolds produced using polyHIPE technology (porous polymers derived from high internal phase emulsions) for routine 3D cell culture applications has generated very promising results in terms of improved replication of native cellular function in the laboratory. These materials, which are now available as commercial scaffolds, are superior to many other 3D cell substrates due to their high porosity, controllable morphology, and suitable mechanical strength. However, until now there have been no reports describing the surface-modification of these materials for enhanced cell adhesion and function. This study, therefore, describes the surface functionalization of these materials with galactose, a carbohydrate known to specifically bind to hepatocytes via the asialoglycoprotein receptor (ASGPR), to further improve hepatocyte adhesion and function when growing on the scaffold. We first modify a typical polystyrene-based polyHIPE to produce a cell culture scaffold carrying pendent activated-ester functionality. This was achieved via the incorporation of pentafluorophenyl acrylate (PFPA) into the initial styrene (STY) emulsion, which upon polymerization formed a polyHIPE with a porosity of 92% and an average void diameter of 33 μm. Histological analysis showed that this polyHIPE was a suitable 3D scaffold for hepatocyte cell culture. Galactose-functionalized scaffolds were then prepared by attaching 2′-aminoethyl-β-d-galactopyranoside to this PFPA functionalized polyHIPE via displacement of the labile pentafluorophenyl group, to yield scaffolds with approximately ca. 7–9% surface carbohydrate. Experiments with primary rat hepatocytes showed that cellular albumin synthesis was greatly enhanced during the initial adhesion/settlement period of cells on the galactose-functionalized material, suggesting that the surface carbohydrates are accessible and selective to cells entering the scaffold. This porous polymer scaffold could, therefore, have important application as a 3D scaffold that offers enhanced hepatocyte adhesion and functionality.

A new parameter for modelling three-dimensional damage evolution validated by synchrotron tomography

Novel methods of correlating damage evolution measurement techniques are explored to produce improved constitutive equations that better account for the effect of initial inclusion distributions on damage softening behaviour. Based on ex situ, high resolution, synchrotron tomographic quantification of the three-dimensional interactions of damage formed during hot deformation of free cutting steel, a new parameter to account for the effect of inclusions on damage is proposed. Uniaxial tensile samples deformed at 1100°C and a strain rate of 0.1s−1 were interrupted at various strains prior to failure. Ex situ synchrotron X-ray computed tomography (sCT) was then used to quantify the growth of damage in the hot deformation of a leaded free cutting steel. Void growth is related to nucleated microvoids at inclusions. The number and volume fraction of voids were calculated for each tensile sample, allowing quantification of the evolving ductile damage via the measured increase in average void diameter after each strain increment. The equivalent diameter, spacing and volume fraction of inclusions were measured at the different interrupt strains. The local strain and stress state, evaluated using the finite element method at the microscale, were related to the local void populations. There was evidence that after necking the damage localized due to clustered inclusions. Damage localization was confirmed with a three-dimensional micromechanics model of 100 inclusions, whose distribution was taken directly from the sCT results, and a novel approach to extract the damage fraction is presented. A new parameter was introduced to account for inclusion size, spacing and clustering, which was validated against the sCT results.

Hydrophilic polymer foams with well‐defined open‐cell structure prepared from pickering high internal phase emulsions

AbstractOpen‐cell hydrophilic polymer foams are prepared through oil‐in‐water Pickering high internal phase emulsions (HIPEs). The Pickering HIPEs are stabilized by commercial titania (TiO2) nanoparticles with adding small amounts of non‐ionic surfactant Tween85. The morphologies, such as average void diameter and interconnectivity, of the foams can be tailored easily by varying the TiO2 nanoparticles and Tween85 concentrations. Further, investigation of the HIPE stability, emulsion structure and the location of TiO2 nanoparticles in resulting foams shows that the surfactant tends to occupy the oil‐water interface at the contact point of adjacent droplets, where the interconnecting pores are hence likely to be formed after the consolidation of the continuous phase. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Synthesis and characterization of a novel poly(vinyl alcohol) 3D platform for the evaluation of hepatocytes' response to drug administration.

Many whole cell-based assays in use today rely on flat, two-dimensional (2D) glass or plastic substrates that may not produce results characteristic of in vivo conditions. In this study, a three-dimensional (3D) cell-based assay scaffold was fabricated using a gas-in-foam templating technique. The scaffold was made of poly(vinyl alcohol), a water-soluble synthetic polymer with excellent film-forming, emulsifying, and biocompatible properties widely used in the biomedical field. The preliminary rheological studies on the solution of PVA and surfactant permitted us to disclose the significant physical parameters that influence the morphology of the ensuing materials. The scaffolds obtained were subjected to detailed analysis by light microscopy, Scanning Electron Microscopy (SEM), computed X-ray microtomography (μCT), infrared spectroscopy, and mechanical testing. Morphological investigations showed that the produced scaffolds are characterised by average void and interconnect diameters lying in the range of 200-300 and 30-150 μm, respectively, suitable for cell infiltration. Two different cross-linking procedures were adopted in order to modulate the mechanical properties of the PVA scaffolds. One made use of a bi-epoxide (PEGDGE), the other was based on glutaraldehyde (GA). The efficiency in terms of cross-linking density of the two procedures resulted in very different mechanical properties. Furthermore, in this article it is demonstrated how PVA foams can be processed into uniform, porous films suitable to be integrated with multi-well 2D culture plates in order to create a 3D analogue. The PEGDGE cross-linked scaffold was tested on C3A cells, a human hepatocyte cell line, representing an appropriate model for liver toxicity studies. Proliferation and cytotoxicity assays indicated good cell viability throughout the culture time, which was also confirmed by SEM analysis. Typical hepatic functions such as albumin and urea production and induction of Cyp3A4 enzyme activity following drug administration were satisfactory, thus proving the efficiency of this construct in maintaining specific liver functions.

Effects of grain size on the dynamic tensile damage of ductile polycrystalline metall

In the paper, we propose a new nucleation rate function, which combines grain size, and models for nucleation and growth of voids in a ductile polycrystalline metal. The proposed model is used to analyse the effects of grain size on the dynamic tensile damage of high purity Cu samples with different grain sizes. Numerical results show that pull-back minima and void number decrease with grain size increasing, slope after pull-back and average void diameter increase with grain size increasing. The computed results are in qualitative agreement with experimental results.

Void evolution in silicon under inert and dry oxidizing ambient annealing and the role of a Si1−xGex epilayer cap

Voids were formed in silicon (Si) and silicon germanium/silicon (Si1−xGex/Si) samples containing 5% or 9% Ge (at. %) by 30 keV, 5 × 1016 cm−2 helium (He+) implantation followed by annealing in nitrogen (N2) or dry oxygen (O2) atmospheres in the temperature range 960–1110 °C. Si1−xGex thicknesses were 60 nm and 20 nm for 5% and 9% Ge, respectively. He+ implantation energy was set such that in Si1−xGex/Si samples voids were formed inside the Si substrate. An increase in annealing temperature resulted in an increase in the average void diameter and decrease in the average void density. Due to the presence of implantation damage and the relatively high temperature anneals, Ge diffusion occurs, which results in a stress gradient in the sample that interacts with the void layer. The presence of Ge also results in weaker Si-Ge bonds (compared to Si-Si bonds). This leads to an increase in the rate of cavity migration providing a likely explanation for the increase in the average void diameter and decrease in the average void density in Si1−xGex/Si samples when compared to the similarly prepared Si samples. No impact on the void evolution process was observed as a result of changing the anneal atmosphere from N2 to dry O2.

Vinyl Ester Oligomer Crosslinked Porous Polymers Prepared via Surfactant‐Free High Internal Phase Emulsions

Using vinyl ester resin (VER) containing styrene (or methyl methacrylate) and vinyl ester oligomer (VEO) as external phase, Pickering high internal phase emulsions (Pickering HIPEs) having internal phase volume fraction of up to 95 vol% were prepared with copolymer particles as sole stabilizer. Polymerizing the external phase of these Pickering HIPEs led to porous polymers (poly‐Pickering‐HIPEs). Compared to the polystyrene‐ (PS‐) based poly‐Pickering‐HIPEs which were prepared with mixture of styrene and divinylbenzene (DVB) as crosslinker, the poly‐Pickering‐HIPEs herein showed much higher elastic modulus and toughness. The elastic modulus of these poly‐Pickering‐HIPEs increased with increasing the VEO concentration in the external phase, while it decreased with increasing internal phase volume fraction. Increasing VEO concentration in the external phase also resulted in a decrease in the average void diameter as well as a narrow void diameter distribution of the resulting poly‐Pickering‐HIPEs. In addition, there were many small pores in the voids surface caused by the volume contraction of VER during the polymerization, which suggests a new method to fabricate porous polymers having a well‐defined hierarchical pore structure.

Stability of surfactant-free high internal phase emulsions and its tailoring morphology of porous polymers based on the emulsions

Stable water-in-oil (w/o) high internal phase emulsions (HIPEs) having an internal phase of up to 95 vol% were prepared. The poly(styrene-methyl methacrylate-acrylic acid) (P(St-MMA-AA)) copolymer particles were used as stabilizer. The HIPEs prepared with addition of copolymer particles to the aqueous phase were stabilized by copolymer particles initially, followed by the mixture of copolymer particles and copolymer as the particles eventually dissolves in the organic phase, and finally by only copolymer. Stable w/o HIPEs having an internal phase of up to 92 vol% were also formed with P(St-MMA-AA) copolymer dissolved in the organic phase as the sole stabilizer. Porous polymers (polyHIPEs) were prepared based on these two types of surfactant-free HIPEs. The morphology of the polyHIPEs, such as the surface roughness of the voids and average void diameter, were tailored by tuning the internal phase volume fraction, NaCl, copolymer, and crosslinker concentrations.

Molecular Voids Formed from Effective Attraction in Submonolayer DNA Deposited on Au(111)

The development of DNA-based biosensors requires a deep understanding of how DNA molecules adsorb and organize on solid state surfaces as well as the electronic properties of individual and aggregates of DNA molecules. Using scanning tunneling microscopy (STM) and atomic force microscopy (AFM), we have successfully characterized an attractive force driven molecular void formation for DNA chemically adsorbed on Au(111) as a function of strand length and deposition conditions. Here we report the observation of these void structures formed on the Au(111) surface by adsorption of both 45 and 90 base pair long, thiolated double-stranded DNA. We found that the average void diameter decreases when increasing the number of base pairs exposed to the surface. The critical determinant in the molecular void formation is the total charge delivered to the surface via the adsorption of the DNA strands and the related counterions, which can ultimately be quantified by the number of base pairs in each adsorbed DNA molecule. Complementary measurements involving STM and AFM suggest that an intact Au(111) surface area is preserved inside the void and is surrounded by a submonolayer of DNA molecules adsorbed on the surface. The discussion of the possible mechanisms for the void formation implies an effective attraction between the DNA molecules.

混合モード荷重下における延性破壊機構の研究 : 第2報,板厚の影響

Three point bend specimen is used for ductile fracture tests with different mixed mode ratio, K_<II>/K_I, and specimen thickness. The crack growth direction in mid-plane of the specimen changes largely with the change of K_<II>/K_I value. Detailed observation of fracture surface is conducted, and it is shown that the average void diameter is affected largely by the mixed mode ratio and specimen thickness. Numerical simulation is also carried out using Gurson's yield function. By introducing stress-controlled void nucleation model, as well as plastic-strain-controlled nucleation model, it is shown that crack growth directions at mid-plane and free surface are estimated well and results agree with experimental observations qualitatively.

Stability of high internal phase emulsions with sole cationic surfactant and its tailoring morphology of porous polymers based on the emulsions

Stable w/o high internal phase emulsion (HIPE) using cetyltrimethylammonium bromide (CTAB) as the sole surfactant was prepared with long time further mixing of the emulsion after the addition of aqueous phase was completed, although it was generally considered the emulsion would be unstable according to Bancroft rule. The delta backscattering data of these emulsions showed that the further mixing enhanced the stability of the HIPE significantly, because a dram partial of monomers was initiated in the period of preparing the emulsion, which reduced the diffusion of CTAB from the oil phase to aqueous phase and increased the viscosity of the continuous phase. In addition, the morphology of polyHIPEs based on this type HIPEs was tailored. Increasing aqueous phase fraction resulted in the increase of pore volume which could be up to 24.0ml/g. Increasing the polymerization temperature led to an increase in average void and interconnect diameter in the resulting porous materials. Additionally, the presence of additives, PEG and ethanol, in the aqueous phase was found to increase the average void diameter remarkably. The interconnect diameter of the materials could be controlled at constant pore volume by tuning PEG and ethanol concentration in the aqueous phase. It was suggested that coalescence was the dominant effect in determining the morphology of the polyHIPEs prepared in the presence of PEG, and Ostwald ripening was the major role in tailoring the morphology of the porous materials with ethanol.

Study on the Ductile Fracture under Mixed Mode Loading Condition

Three point bend specimen is used for ductile fracture tests with different mixed mode ratio, KII/KI. The crack growth direction in mid-plane of the specimen changes largely with the change of KII/KI value. Detailed observation of fracture surface is conducted, and it is shown that the average void diameter becomes smaller as KII/KI becomes lager. Numerical simulation is also carried out using Gurson's yield function. By introducing stress-controlled void nucleation model, as well as plastic-strain-controlled nucleation model, it is shown that crack growth directions at mid-plane and tree surface are estimated well and results agree with experimental observations qualitatively. Distributions of stress triaxiality and plastic strain are also evaluated and their effects on dimple fracture process are discussed.

Emulsion-templated porous polymers as scaffolds for three dimensional cell culture: effect of synthesis parameters on scaffold formation and homogeneity

Emulsion-templated porous polymers (PolyHIPEs) based on polystyrene have been prepared and used for in vitro 3D cell culture of osteoblastic cells. It has been found that the method employed to prepare the emulsion precursor, namely the method of aqueous phase addition, has a significant influence on the homogeneity of the morphology of the material produced as well as the reproducibility of preparation. Addition of the aqueous phase in a controlled manner by means of a syringe pump produced a narrower void size distribution range than addition from a dropping funnel, and the emulsions were obtained in a reproducible manner. Analysis of the morphology of the materials revealed consistency of average void and interconnect diameter, within certain limits. The materials produced were subsequently sectioned into thin membranes which were then mounted to the base of commercially available tissue culture plastic well inserts. Cell culture experiments using MG63 osteoblast-like cells indicated that the materials were capable of supporting cell growth for periods of up to 35 days, producing complex arrangements of cells interacting with one another and the scaffold. The functionality of cells grown on these materials, as indicated by viability assays and the production of biomarkers (alkaline phosphatase and osteocalcin), was found to be enhanced compared to cells grown on 2D substrates. We conclude that the 3D environment produced by these porous materials is more conducive to cell growth in vitro than existing 2D culture plastic.

Aspects of the preparation of starch microcellular foam particles crosslinked with glutaraldehyde using a solvent exchange technique

Starch microcellular foam (SMCF) has been produced using a solvent exchange technique with a native corn starch crosslinked with glutaraldehyde. To produce a high specific surface area for the starch particles the cooked starch solution was reacted with glutaraldehyde and then precipitated under shear with ethanol. The relationship between the crosslinking density on the void structure of the SMCF has been studied. Characterization by NMR confirmed the crosslinking reaction. An increase in the glutaraldehyde concentration from 0 to 15 g glutaraldehyde/100 g starch was accompanied by a decrease in particle size and moisture content and an increase in brightness and specific surface area. Scanning electron microscope images of the SMCF particles show that the smallest average void diameter obtained was 0.182 μm at a 7.5 g glutaraldehyde/100 g starch. Four starch materials having different viscosity were prepared by hydrolysis of the native corn starch with a 1 N HCl/methanol system for different reaction durations to investigate the relationship between starch molecular weight and void structure of the SMCF. The starches were crosslinked with 15 g glutaraldehyde/100 g starch and precipitated with ethanol to form SMCF. Decreasing the starch viscosity decreased the brightness and specific surface area, and increased the particle size, void diameter and moisture content. Increases in stirring speed during the precipitation enhanced the properties of the SMCF particles. The effect of pressing the starch particles to form a pellet caused a collapse of the foam structure at pressures above about 6000 psi. The results indicate that the structure/chemistry of the starch material and the processing conditions can be controlled in order to produce particles with morphology and properties useful for light scattering applications. In particular, higher molecular weight and intermolecular crosslinking and high shear during precipitation have been found to enhance the foam formation.