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1.
E. Rudnik I. Resiak C. Wojciechowski Z. Dobkowski 《Journal of Thermal Analysis and Calorimetry》2001,64(2):495-500
Laboratory-made asymmetric polyurethane membranes designed for immunoisolation were investigated. Two types of EK and ES membranes
were prepared in different spinning conditions.
The membrane structure was characterised by the skin pore radius measurements using differential scanning calorimetry (DSC).
Diffusive transport properties of membranes were determined by in vitro method for albumin and creatinine. The scanning electron
microscopy (SEM) was applied to study the morphology of membranes.
It has been found that the DSC technique is a useful tool for the evaluation of pore radii in the skin layer for PU membranes.
Calculated pore radii were in the range from 1.95 to 2.47 nm for the EK and ES types. A correlation between the skin pore
radii and the transport properties was not found in this case of investigated membranes. However, the transport properties
data can serve for the estimation of selectivity of membranes. Thus, the selectivity of membranes for solutes of various molecular
size was estimated from the D
m/D
w ratio of diffusion coefficients for albumin and creatinine. The SEM micrographs reveal the finger-like internal structure
of capillary membranes, as well as various skin thickness.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
Dr. Zbigniew Dobkowski 《Rheologica Acta》1995,34(6):578-585
The multivariable power dependence of polymer properties on molecular characteristics (Dobkowski, 1981) has been applied to molecular weight dependence of tensile strength, and the known equation of Flory (1945) has been extended taking polydispersity of polymers into account. Constant parameters of the relevant regression equations have been calculated using experimental data on tensile strength and molecular weight averagesM
n andM
w of polystyrene (PS) and polycarbonate (PC). Then, the critical molecular weight for entanglementsM
c has been obtained from the following relationship:A=K
M
cwhereA and are parameters of the extended Flory equation for the tensile strength, and the constantK = 2 is assumed for linear polymers. It has been found thatM
c of injection and compression moulded PS is equal to 34000 and 37350g/mole, respectively, whileM
c of injection moulded PC equals to 5000 g/mole. The values ofM
c calculated from the polymer tensile strength are consistent with published data obtained by other methods and with the computer modeling calculations. Branched polymers have only qualitatively been discussed. Dimensionless equations have been proposed for tensile strength characteristics for polymer materials.The described procedure can be suggested as applicable to various polymers for the determination of theirM
c values. However, more experimental data on another polymer materials will be necessary to support hitherto obtained results.The essential part of a lecture presented during the NATO Advanced Study Institute Rheological Fundamentals of Polymer Processing, Alvor, Portugal, 26 September–7 October 1994 相似文献
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Z. Dobkowski 《European Polymer Journal》1982,18(7):563-567
Molecular weight distribution and long chain branching were taken into account for the glass transition temperature (Tg)-molecular weight (M) relationships for bisphenol-A polycarbonate. A new form of the four-variable equation for Tg is proposed for polydisperse branched polymers. The extended equations were compared with the experimental results on Tg and M averages; they were also applied for characterization of branched polymer by the combined GPC/V and DSC methods. 相似文献
5.
S. Dähne W. Freyer K. Teuchner J. Dobkowski Z.R. Grabowski 《Journal of luminescence》1980,22(1):37-49
p-Dimethylaminobenzaldehyde (DMABA, I) and its N-to-N trimethylene-bridged double molecule (III) exhibit dual or multiple fluorescences. Several mechanisms were proved to be responsible for the long-wave fluorescence bands: intramolecular solvent-assisted relaxation in the excited state (I and III); ground state aggregation at low temperatures (I in nonpolar solvents); excimer formation (III; and I only at high concentrations in some solvents). Intramolecular interaction in the ground state of III prepares an excimer-like structure. The dimer of DMBA aside of its own emission, may relax and emit an excimer-like fluorescence. 相似文献
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Z. Dobkowski 《European Polymer Journal》1984,20(4):399-403
Linear and branched bisphenol A polycarbonate (PC) samples were characterized by their average molecular weights, and , polydispersity degree , and branching degree gv. The weight fraction of microgel was also determined for branched samples. The samples were amorphized and densities were measured at 23°C to obtain the values of specific volume, vsp. The dependence of vsp on molecular characteristics is described by the multivariable power function , where Δvsp = vsp ? vsp,∞, and Asp, a, apx and ab are constants. It has been confirmed that a = ?1, apn = 0 and apw = 1. It has also been found that the branching exponent ab significantly depends on microgel content. The relationships found for PC should, in principle, be valid for other polymers. Examples based on literature data are given for linear polyethylene and polydimethylsiloxane. 相似文献
8.
Gel permeation chromatography (GPC) and viscometry (V) methods have been combined for determination of long-chain branching in bisphenol-A polycarbonate (PC) by means of a branching factor , where and are the apparent viscosity-average molecular weights calculated from GPC data and from intrinsic viscosities [η] of the samples respectively. A linear dependence of gv on molar % of branching agent has been obtained. The GPC data on PC samples have also been applied for verification of an earlier [η]?M relationship for branched polydisperse polymers. 相似文献
9.
Piotr Mucha Jaroslaw Ruczynski Michal Dobkowski Ewelina Backtrog Piotr Rekowski 《Electrophoresis》2019,40(2):336-342
Systemin (Sys) is an 18‐aa plant peptide hormone involved in the regulation of plant's defensive response. Sys is considered as a fast‐spreading systemic wound signal. We developed a simple and rapid CE method to monitor the spreading of Sys peptides through tomato plant. A 1,2,3‐triazole‐linked AZT‐systemin conjugate was designed as a model to study the possibility of translocating small cargo molecules 3'‐Azido‐2',3'‐dideoxythymidine by systemin. The Sys peptides (Sys, N‐propiolyl Sys, and AZT‐systemin conjugate) were injected into the stem and leaves of mature tomato plant. Its transportation throughout the plant tissue was traced by CE. The peptides were clearly visible in the crude tomato exudates and an optimum separation was achieved in 25 mM phosphate “buffer” at pH 2.5 and a voltage of 20 kV using uncoated fused silica capillary. CE analysis showed that Sys peptides are well separated from tomato plant exudates ingredients and are stable in tomato stem and leaf exudates for up to 24 h. CE study revealed that the Sys peptides are effectively spreading throughout tomato stem and leaves and the peptides could be directly detected in the crude plant matrixes. The translocation was strongly inhibited by sodium azide. The results showed that the established CE method can be used to characterize plant peptides spreading under plant physiological conditions. 相似文献
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