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1.
For a liquid-crystalline side chain polymer with cyanobiphenyl mesogenic groups and a spacer length of four methylene groups the dielectric properties over a wide frequency range are studied. They are compared with a previously published analogous compound with six spacer groups in order to get the spacer length dependence of dielectric relaxations. Both compounds have been analysed in terms of theoretical relaxation curves. The δ-relaxation is more asymmetrically broadened and shifted to longer relaxation times for shorter spacer. This is consistent with its molecular interpretation as end-to-end rotation around the short molecular axis. The relaxation in perpendicular orientation is strongly shifted to longer relaxation times and shows another temperature dependence for shorter spacer. This behaviour is attributed to superposition of up to three separate relaxation processes. 相似文献
2.
A suite of aromatic hydrocarbons were used to investigate the influence of structure upon retention in normal-phase HPLC mode using bare silica and aminopropyl-modified silica Chromolith type monolithic columns. The aminopropyl-modified silica monolith was used to separate a complex petroleum fraction based on double bond equivalence. 相似文献
3.
《Liquid crystals》2012,39(15):2201-2212
ABSTRACTFour compounds from 3FmHPhF homologous series of chiral smectogenic fluorinated compounds (m = 2, 4, 5, 6) were studied by frequency domain dielectric spectroscopy, electro-optic measurements, X-ray diffraction and differential scanning calorimetry. Values of the relaxation time and dielectric increment of relaxation processes versus temperature and bias field were determined. The temperature-dependent tilt angles, spontaneous polarisations, switching times, rotational viscosities, and average intermolecular distances and correlation lengths within smectic layers were obtained. Experimental results were supplemented by density functional theory calculations of isolated 3FmHPhF molecular geometries, and the relationship between the molecular structures and the transverse component of their dipole moments was studied for the mesogens with m = 2, 4, 5, 6, 7. The results are discussed in terms of the length of the CmH2m flexible carbon chain of the homologues. 相似文献
4.
Influence of surfactant surface coverage and aging time on physical properties of silica nanoparticles 总被引:1,自引:0,他引:1
Gui-Mei Gao Hai-Feng Zou Da-Rui Liu Li-Na Miao Gui-Juan Ji Shu-Cai Gan 《Colloids and surfaces. A, Physicochemical and engineering aspects》2009,350(1-3):33-37
The experimental results on the influence of surfactant surface coverage and aging time on physical properties of silica nanoparticles were reported. The spherical silica nanoparticles have been synthesized using polyethylene glycol (PEG) as the surfactant and oil shale ash (OSA) as a new silica source. In order to identify the optimal condition for producing the best quality silica nanoparticles with the good dispersion and uniformity, the effects of surfactant surface coverage and aging time were investigated. It was found that the particle size and distribution of silica nanoparticles depend on the concentration of PEG in dispersion. At relatively low concentration, 0–2 wt.%, the existing PEG is not sufficient to prevent further growth of the initially formed silica nanoparticles, leading to large aggregates of silica particles. When the PEG concentration increases to 3 wt.%, self-assembled PEG layer on the surface stabilizes the initially formed silica nanoparticles and the silica particles with average diameter of 10 nm are uniformly distributed. With further increasing the concentration of PEG, the number of PEG aggregates increases and silica nanoparticles are mainly formed inside the entangled PEG chains, resulting in an observation of clusters of silica nanoparticles. Moreover, it was found that as the aging time increased, the shape of silica nanoparticles becomes regular and the particle size distribution becomes narrow. 相似文献
5.
A series of dissymmetric gemini imidazolium surfactants with different spacer length ([CmCsCnim]Br2, m + n = 24, m = 12, 14, 16, 18; s = 2, 4, 6) were synthesized and characterized by 1H NMR and ESI-MS spectroscopy. Their adsorption and thermodynamic properties were investigated by the surface tension and electrical conductivity methods. Consequently, the surface activity parameters (cmc, γcmc, πcmc, pC20, cmc/C20, Γmax, Amin) and thermodynamic parameters (ΔGmθ, ΔHmθ, ΔSmθ) were obtained. The effects of the dissymmetry (m/n) and the spacer length (s) on the surface activity and micellization process of surfactants have been discussed in detail. 相似文献
6.
Aurlien Guyard Jacques Persello Jean‐Philippe Boisvert Bernard Cabane 《Journal of Polymer Science.Polymer Physics》2006,44(7):1134-1146
Cast film composites have been prepared from aqueous polymer solutions containing nanometric silica particles. The polymers were polyvinyl alcohol (PVA), hydroxypropylmethylcellulose (HPMC) and a blend of PVA‐HPMC polymers. In the aqueous dispersions, the polymer–silica interactions were studied through adsorption isotherms. These experiments indicated that HPMC has a high affinity for silica surfaces, and can adsorb at high coverage; conversely, low affinity and low coverage were found in the case of PVA. In the films, the organization of silica particles was investigated through transmission electron microscopy (TEM) and small‐angle neutron scattering (SANS). Both methods showed that the silica particles were well‐dispersed in the HPMC films and aggregated in the PVA films. The mechanical properties of the composite films were evaluated using tensile strength measurements. Both polymers were solid materials, with a high‐elastic modulus (65 MPa for HPMC and 291 for PVA) and a low‐maximum elongation at break (0.15 mm for HPMC and 4.12 mm for PVA). In HPMC films, the presence of silica particles led to an increase in the modulus and a decrease in the stress at break. In PVA films, the modulus decreased but the stress at break increased upon adding silica. Accordingly, the polymer/silica interaction can be used to tune the mechanical properties of such composite films. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1134–1146, 2006 相似文献
7.
Guangwu Liu Bin Zhou Xingyuan Ni Jun Shen Guangming Wu Ai Du Guoqing Zu 《Journal of Sol-Gel Science and Technology》2012,62(2):126-133
The experimental results of thermal process on the microstructural and physical properties of ambient pressure dried hydrophobic
silica aerogel monoliths are reported and discussed. With sodium silicate as precursor, ethanol/hexamethyldisiloxane/hydrochloric
acid as surface modification agent, the crack-free and high hydrophobic silica aerogel monoliths was obtained possessing the
properties as low density (0.096 g/cm3), high surface area (651 m2/g), high hydrophobicity (~147°) and low thermal conductivity (0.0217 Wm/K). Silica aerogels maintained hydrophobic behavior
up to 430 °C. After a thermal process changing from room temperature to 300 °C, the hydrophobicity remained unchanged (~128°),
of which the porosity was 95.69% and specific density about 0.094 g/cm3. After high temperature treatment (300–500 °C), the density of final product decreased from 0.094 to 0.089 g/cm3 and porosity increased to 96.33%. With surface area of 466 m2/g, porosity of 91.21% and density about 0.113 g/cm3, silica aerogels were at a good state at 800 °C. Thermal conductivities at desired temperatures were analyzed by the transient
plane heat source method. Thermal conductivity coefficients of silica aerogel monoliths changed from 0.0217 to 0.0981 Wm/K
as temperature increased to 800 °C, revealed an excellent heat insulation effect during thermal process. 相似文献
8.
The liquid crystalline properties of two series of non-symmetric liquid crystal dimers consisting of cholesterol and Schiff base moieties interconnected by ω-oxyalkanoyl spacers of varying length are compared: one series (SBOC- n ) carry the octyloxy tail on the Schiff base mesogen, and the other (SBOF- n ) a perfluoroheptylmethyloxy tail. In general, compounds with the fluorinated alkoxy tail exhibited mesophases over a much wider temperature range than those with the alkoxy tail. The latter series favoured the formation of more diverse mesophases than the former. SBOC-4, -5 and -7, and SBOF-4, -5 and -10 formed the chiral smectic C phase. 相似文献
9.
The liquid crystalline properties of two series of non‐symmetric liquid crystal dimers consisting of cholesterol and Schiff base moieties interconnected by ω‐oxyalkanoyl spacers of varying length are compared: one series (SBOC‐ n ) carry the octyloxy tail on the Schiff base mesogen, and the other (SBOF‐ n ) a perfluoroheptylmethyloxy tail. In general, compounds with the fluorinated alkoxy tail exhibited mesophases over a much wider temperature range than those with the alkoxy tail. The latter series favoured the formation of more diverse mesophases than the former. SBOC‐4, ‐5 and ‐7, and SBOF‐4, ‐5 and ‐10 formed the chiral smectic C phase. 相似文献
10.
Mingqi Ao Peipei Huang Guiying Xu Xiaodeng Yang Yajing Wang 《Colloid and polymer science》2009,287(4):395-402
The aggregation behavior and thermodynamic properties of micellization for the ionic liquid-type gemini imidazolium surfactants
with different spacer length ([C12–s–C12im]Br2, s = 2, 4, 6) have been investigated by means of surface tension, electrical conductivity, dynamic light scattering and fluorescence
measurements. The values of cmc, γ
cmc, Γ
max, A
min, π
cmc, pc20 and cmc/pc20 suggest that the shorter the spacer, the higher the surface activity of [C12–s–C12im]Br2 is. The cmc and γ
cmc values are decreased significantly in the presence of sodium halides, and the values decrease in the order NaCl < NaBr < NaI.
The thermodynamic parameters of micellization (, , ) indicate that the micellization of [C12–2–C12im]Br2 and [C12–4–C12im]Br2 is entropy-driven, whereas aggregation of [C12–6–C12im]Br2 is enthalpy-driven at lower temperature but entropy-driven at higher temperature. Finally, the fluorescence measurements
show that the micropolarity of micelles increases but the aggregation numbers decrease with increasing the spacer length of
[C12–s–C12im]Br2. 相似文献
11.
12.
Micaèle Gelhausen Françoise Besson Sabine Chierici Dominique Lafont Paul Boullanger Bernard Roux 《Colloids and surfaces. B, Biointerfaces》1998,10(6):1828-404
Eleven neoglycolipids were synthesized with a membrane anchor (cholesterol or Guerbet alcohols) attached, via a hydrophilic spacer, to a potential lectin-recognized sugar moiety (N-acetylglucosamine: GlcNAc). Neoglycolipids G24-0, G28-0 and G32-0, with a C24, C28 and C32 Guerbet alcohol residue, had no spacer, while neoglycolipids G24-3, G28-3, G32-3 contained a triethoxy spacer. Cholesteryl neoglycolipids chol-1 to chol-4 and chol-7 contained one to four and seven ethoxy units. All the cholesteryl neoglycolipids were incorporated into liposomes, while, for the Guerbet derivatives, the presence (or not) of a spacer and the length of their alkyl chains played an important role for obtaining mixed liposomes. The abilities of liposomes to be recognized by wheat germ agglutinin (WGA) were measured as an increase of the absorbance at 450 nm. Significant WGA-induced aggregations were obtained with liposomes containing neoglycolipids chol-3, chol-4, chol-7, G28-3 and G32-3. As neoglycolipid G24-3 was not recognized, the accessibility of its GlcNAc moiety for WGA depended not only on the spacer length but on the nature of the anchor. The WGA-induced aggregations increased with increasing lectin concentrations until a maximum value, which depended on the nature of the neoglycolipid. The highest aggregation obtained with G28-3 and G32-3 occurred for a WGA–neoglycolipid mole ratio superior to the ratio observed with chol-3, chol-4 and chol-7. A preincubation of WGA with free GlcNAc did not inhibit the aggregation between WGA and mixed liposomes, demonstrating a greater affinity of WGA for the neoglycolipid GlcNAc than for free GlcNAc. 相似文献
13.
T Nakagawa A Shibukawa N Shimono T Kawashima H Tanaka J Haginaka 《Journal of chromatography. A》1987,420(2):297-311
The properties of internal-surface reversed-phase silica packings developed for use in high-performance liquid chromatography, were investigated with regard to the effects of mobile phase conditions (pH, ionic strength, nature and concentration of organic modifiers, ion-pairing agent and surfactant) on the retention of some selected compounds having different polarities. The results indicated that pi-electron interactions play the main role in solute retention, although it is weaker than that on phenylsilica supports, and that weak cation-exchange properties exert a secondary effect on the retention of ionic solutes. The ion-pairing effect was found to be markedly weakened in mobile phases containing an anionic counter ion. In contrast, the addition of a surfactant (SDS) caused a marked increase in the retention of certain drugs at low pH and expanded the pH range of the mobile phase applicable to plasma samples. Based on these findings, the separation and recovery of several drugs (probenecid, lidocaine, cefpiramide and cefaclor) from human plasma were investigated, with emphasis on their protein bindings. The contour chromatogram of human plasma is also demonstrated in relation to the selection of the detection wavelength. 相似文献
14.
《Journal of molecular catalysis. A, Chemical》2000,151(1-2):225-231
Mesostructured silicas and silicates have been synthesized using hydrogels with molar composition: M:26.0SiO2:5.2(C2H5)4NOH:7.5[CH3(CH2)15N(CH3)3]2O:790H2O, where M=0, Zr(OC3H7)4 or Ti(OC4H9)4. In all preparations, colloidal silica (Ludox) was used as the source of silica. The hydrothermal transformation at 110°C of these gels produced solids with the hexagonal structure typical of MCM-41 type materials. The effects of chain length and surfactant terminal alkyl groups on the properties of mesoporous materials containing Ti or Zr, have been investigated by using different surfactants such as cetyl trimethyl ammonium bromide and chloride, cetyl dimethyl ethyl ammonium bromide, and myristyl trimethyl ammonium bromide. When the surfactant's carbonyl chain decreased to 14 from 16 carbon atoms, a reduction in unit cell dimension and average pore diameter was observed in the mesoporous silicas, titaniumsilicates and zirconiumsilicates under study. Replacement of methyl groups with ethyl groups on the surfactant hydrophobic head, had no measurable effects on crystals' properties. However, a surfactant with a bulky aromatic head group, such as cetyl pyridinium chloride, inhibited crystallization. In general, the use of bromide in place of chloride salts yielded more ordered MCM-41 type crystals. The high thermal stability (to 800°C), surface area (1000–1500 m2/g), pore volume (0.90–1.20 cm3/g) and uniform mesoporosity (with pore diameter in the 2.9 nm–3.6 nm range), of these metalsilicates could be of particular interest in the preparation of catalysts requiring siliceous metal supports. 相似文献
15.
R. Peña-Alonso L. Téllez J. Rubio F. Rubio 《Journal of Sol-Gel Science and Technology》2006,38(2):133-145
The application of nitrogen adsorption, mercury porosimetry and inverse gas chromatography (IGC) for the examination of surface
physical and chemical properties of hybrid materials is discussed. Hybrid materials were prepared from tetraethoxysilane (TEOS),
tetrabutyl orthotitanate (TBOT), and hydroxyl terminated polydimethyl siloxane (PDMS) for different TBOT concentrations. It
was found that TBOT affects specific surface areas, pore volumes and pore sizes, but does not affect pore morphology. Surface
chemical properties were analyzed by IGC. It was found that the dispersive surface energy was a function of the material pore
size. Values between 36 and 42 mJ···m-2 were obtained for the dispersive surface energy which are consistent with those of hybrid materials. On the other hand, the
acid-base (k
, k
) surface constants showed good correlation with the TBOT concentration. These materials can be considered as anphoteric ones,
and it was found that k
increases from 1.07 to 1.47, and k
increases from 0.76 to 1.73 when the TBOT concentration increases from 0 to 7%. Such increase is assigned to the formation
of Si–O–Ti bonds as it was deduced from an IR band appearing at 930 cm-1 in the FT-IR spectra. 相似文献
16.
Phthalocyanines R, PcM (R = alkyl, M = H, Ni, Cu) substituted with alkyl chains have been synthesized and their liquid crystalline properties studied by differential scanning calorimetry and X-ray diffraction at small angles. The influence of the chain length on the mesomorphic properties has been determined. A model is proposed to rationalize the structural modifications induced by varying the nature of the connecting link between the macrocycle and the side chains (alkyl, alkoxymethyl, alkoxy). 相似文献
17.
Effects of polyethylene spacer length in polymeric electrolytes on gelation of ionic liquids and ionogel properties
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Jun'ichi Nagasawa Sonoko Wakahara Hajime Matsumoto Hideyuki Kihara Masaru Yoshida 《Journal of polymer science. Part A, Polymer chemistry》2015,53(2):249-255
Polymer electrolytes containing N,N′-(trans-cyclohexane-1,4-diyl)dibenzamide linkages, polyethylene ((CH2)m, m = 2, 4, 10) spacers, and bis(trifluoromethanesulfonyl)amide (TFSA) or bis(fluorosulfonyl)amide (FSA) counteranions (polymer abbreviation: CDBAm•X; m = 2, 4, 10; X = TFSA, FSA) have been synthesized, adding to our previous report (m = 6). In addition, their ability to effect the gelation of six ionic liquids and the properties of the resulting ionogels have been examined. The polymers, except for CDBA10•TFSA, effect the gelation for all ionic liquids used in this study at fairly low concentrations (0.9–50 g/L). Ionogel ionic conductivity is not dependent on the spacer length, but does decrease slightly as increasing amounts of the gelatinizer are introduced. In contrast to ionic conductivity, the temperatures at which these ionogels transition into isotropic fluids is dependent on the spacer length; the gel composed of [EMI][FSA] and 100 g/L of CDBA6•FSA transforms at 120 °C, while the gel composed of [EMI][FSA] and 5 g/L of CDBA2•FSA does not transform into a sol even when temperatures become 155 °C. In brief, ionogel heat resistance can be improved by changing the spacer length of the polyelectrolyte. Finally, it has been determined using cyclic voltammetry that the potential window of the polyelectrolytes is particularly wide, ranging from −1.6 to 2.5 V. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 249–255 相似文献
18.
The chromatographic performance of a new brand of shell particles is compared to that of a conventional brand of totally porous silica particles having a similar size. The new material (Halo, Advanced Materials Technology, Wilmington, DE) is made of 2.7 microm particles that consist in a 1.7 microm solid core covered with a 0.5 microm thick shell of porous silica. The other material consists of the porous particles of a conventional 3 microm commercial silica-B material. These two columns have the same dimensions, 150 mm x 4.6mm. The reduced plate heights of two low molecular weight compounds, naphthalene and anthracene, two peptides (lys-bradykinin and bradykinin), and four proteins, insulin, lysozyme, beta-lactoglobulin, and bovine serum albumin were measured in a wide flow rate range and analyzed on the basis of the Van Deemter equation and of modern models for its terms. The Halo column provides a smaller axial diffusion coefficient B and a smaller eddy dispersion term A than the other column, a result consistent with its lower internal porosity (in(p)=0.19 versus 0.42) and with the narrower size distribution of its particles (sigma=5% versus 13%). The two columns have similar C terms for the two low molecular weight compounds and for the two peptides. However, the C term of the proteins that are not excluded is markedly lower on the column packed with the Halo particles than on the other column. A recent theoretical analysis of the mass transfer kinetics in shell particles predicts a C term for moderately retained proteins (3相似文献
19.
酯化硅胶的物理结构和表面性质的研究 总被引:3,自引:0,他引:3
本文利用正庚醇或正辛醇与硅胶表面羟基反应制备了酯化硅胶。测定了酯化硅胶的物理结构、水蒸气吸附等温线、润湿热、差热分析和红外光谱。结果表明: (1)所有酯化硅胶的真密度(dT)、比表面(S)和比孔体积(V)均减少, 而有观密度(dA)增加, 但平均孔半径(r)变化不大; (2)酯化硅胶是憎水的, 其对水蒸气吸附, 以及对水和环己烷的润湿热均显著减少; (3)酯化硅胶的表面酯基在空气中于235-350℃破坏; (4)酯化反应是可逆的, 硅胶表面酯基在水中大约可水解41-47%。 相似文献
20.
本文利用苯基三氯硅烷和硅胶表面羟基反应制备了苯基化硅胶。测定了苯基化硅胶的物理结构、水蒸气吸附等温线、润湿热、差热分析(DTA)和红外光谱(IR)。结果表明,所有苯基化硅胶的真密度(dT)、比表面(S)和比孔体积(V)均减少, 而表观密度(dA)增加, 但苯基化对不同硅胶的平均孔半径(r)有不同的影响; 苯基化硅胶对水蒸气吸附, 对水、苯和环己烷的润湿热均显著减少; 苯基化硅胶的热稳定性大于甲基化硅胶, 甲基化硅胶的表面是高度憎水的, 但苯基化硅胶的憎水性则很弱。 相似文献