Dielectric Relaxation Based on Adsorbed Water in Wood Cell Wall under Non-Equilibrium State. 1

Holzforschung ◽  
2000 ◽  
Vol 54 (3) ◽  
pp. 321-326 ◽  
Author(s):  
Cao Jinzhen ◽  
Zhao Guangjie
Keyword(s):  
Cell Wall ◽  
Dielectric Relaxation ◽  
Relaxation Process ◽  
Wood Cell Wall ◽  
Adsorbed Water ◽  
Amorphous Region ◽  
Oh Groups ◽  
Adsorption Processes ◽  
Initial Adsorption ◽  
State 1

Summary In order to make clear the molecular mechanism of the dielectric relaxation based on adsorbed water in wood cell wall during moisture changing process, the temperature and frequency spectrums of dielectric processes of Sikkim spruce (Picea spinulosa Griff.) were measured in three different adsorption processes. Three levels of relative humidity used were 40, 80 and 100 %, respectively, and the temperature was kept at 20°C. In oven-dry state, relaxation process I based on the reorientation of CH2OH groups in amorphous region of wood cell wall was observed. While in moist state, relaxation process II based on ionic conductivity and relaxation process III based on the additive reorientation of CH2OH groups and adsorbed water molecules occurred. Within higher humidity region, relaxation process IV concerned with adsorbed water in lignin was observed in the initial adsorption period, but it vanished with further adsorption.

Dielectric Relaxation Based on Adsorbed Water in Wood Cell Wall under Non-Equilibrium State 2

Holzforschung ◽  
2001 ◽  
Vol 55 (1) ◽  
pp. 87-92 ◽  
Author(s):  
C. Jinzhen ◽  
Z. Guangjie
Keyword(s):  
Cell Wall ◽  
Equilibrium State ◽  
Dielectric Relaxation ◽  
Adsorption Process ◽  
Wood Cell Wall ◽  
Adsorbed Water ◽  
Thermodynamic Quantities ◽  
Frequency Spectra ◽  
Adsorption Sites ◽  
Non Equilibrium

Summary In order to explain, on molecular level, the unusualness of wood physical properties under moisture non-equilibrium state, the dielectric temperature and frequency spectra of Sikkim spruce (Picea spinulosa Griff.) specimens were measured during the adsorption process in 20°C, 60% R.H. environment. Furthermore, the dielectric relaxation based on adsorbed water was separated from that based on the methanol groups in the amorphous region of wood cell wall, so that the thermodynamic quantities of adsorbed water associated with the adsorption process could be evaluated. Consequently, the molecular reorientation model of adsorbed water molecules during the dielectric relaxation process was constructed. The results show that the activation enthalpy ∆H and activation entropy ∆S of adsorbed water both increase linearly with the adsorption time. During the initial adsorption period ∆S appears as a negative value. According to the values of thermodynamic quantities, especially the ∆H values, it can be inferred that the average number of hydrogen bonds formed between each adsorbed water molecule with its surrounding wood adsorption sites increases gradually with developing adsorption. The model based on the obtained data in this experiment shows that after 7 hours' adsorption the number is between two and three, after 24 hours it is three and later it approaches four.

Dielectric Relaxation Studies of Silver Nanoparticles dispersed Liquid Crystal

2015 ◽  
Vol 8 (3) ◽  
pp. 2176-2188 ◽  
Author(s):  
Keisham Nanao Singh
Keyword(s):  
Activation Energy ◽  
Silver Nanoparticles ◽  
Liquid Crystal ◽  
Dielectric Relaxation ◽  
Relaxation Process ◽  
Relaxation Times ◽  
Low Frequency ◽  
Bulk Liquid ◽  
Molecular Rearrangement ◽  
Relaxation Studies

This article reports on the Dielectric Relaxation Studies of two Liquid Crystalline compounds - 7O.4 and 7O.6 - doped with dodecanethiol capped Silver Nanoparticles. The liquid crystal molecules are aligned homeotropically using CTAB. The low frequency relaxation process occurring above 1 MHz is fitted to Cole-Cole formula using the software Dielectric Spectra fit. The effect of the Silver Nanoparticles on the molecular dipole dynamics are discussed in terms of the fitted relaxation times, Cole-Cole distribution parameter and activation energy. The study indicate a local molecular rearrangement of the liquid crystal molecules without affecting the order of the bulk liquid crystal molecules but these local molecules surrounding the Silver Nanoparticles do not contribute to the relaxation process in the studied frequency range. The observed effect on activation energy suggests a change in interaction between the nanoparticles/liquid crystal molecules.

scholarly journals PVDF-HFP/NKBT composite dielectrics: Perovskite particles induce the appearance of an additional dielectric relaxation process in ferroelectric polymer matrix

2021 ◽  
Vol 96 ◽  
pp. 107093
Author(s):  
Vera P. Pavlović ◽  
Dragana Tošić ◽  
Radovan Dojčilović ◽  
Duško Dudić ◽  
Miroslav D. Dramićanin ◽  
...  
Keyword(s):  
Dielectric Relaxation ◽  
Relaxation Process ◽  
Polymer Matrix ◽  
Dielectric Relaxation Process ◽  
Ferroelectric Polymer

Acetyl Group Distribution in Acetylated Wood Investigated by Microautoradiography

Holzforschung ◽  
2001 ◽  
Vol 55 (3) ◽  
pp. 270-275 ◽  
Author(s):  
Marie Rosenqvist
Keyword(s):  
Cell Wall ◽  
Weight Gain ◽  
Acetic Anhydride ◽  
Wood Cell Wall ◽  
Environmental Scanning Electron Microscopy ◽  
Environmental Scanning ◽  
Accurate Information ◽  
Concentration Gradients ◽  
Good Opportunity ◽  
Acetyl Group

Summary Sapwood of Scots pine (Pinus silvestris L.) was acetylated with 14C- and 3H-labelled acetic anhydride. The distribution of acetyl groups was investigated with microautoradiography and microautoradiographs were evaluated with ESEM, Environmental Scanning Electron Microscopy. The investigation showed that the impregnation of wood with radioisotope-labelled substances provides a good opportunity to investigate the location of substances covalently bonded to the wood material. Introduced 14C-labelled acetyl groups show an even distribution in the wood cell wall, with no discernible concentration gradients at acetylation levels of about 5, 15 and 20% weight gain. 3H-labelled acetyl groups show an even distribution in the wood cell wall at 15 and 20% weight gain, with no discernible concentration gradients. At the 5% weight gain level, however, an uneven distribution of 3H-labelled acetyl groups over the cell wall is observed. Nevertheless, the unevenness is random and no concentration gradient is discernible at this level. 3H with a relatively high resolution, 0.5–1 μm, compared to 14C with a resolution of 2–5 μm, gives more accurate information about where exactly the acetyl groups are situated in the wood cell wall. Acetic anhydride was evenly distributed when a full impregnation procedure was used. The chemical and physical properties of acetic anhydride allow a uniform penetration into the pine cell wall and a complete acetylation takes place when the specimens are heated.

scholarly journals Water and Carbon Dioxide Adsorption on CaO(001) Studied via Single Crystal Adsorption Calorimetry

2021 ◽  
Author(s):  
J. Seifert ◽  
S. J. Carey ◽  
S. Schauermann ◽  
S. Shaikhutdinov ◽  
H.-J. Freund
Keyword(s):  
Adsorption Energy ◽  
Adsorbed Water ◽  
Spectroscopic Studies ◽  
Detector Response ◽  
Adsorption Calorimetry ◽  
Instrument Response Function ◽  
Line Shapes ◽  
Adsorption Sites ◽  
Saturation Coverage ◽  
Initial Adsorption

AbstractA new method to analyze microcalorimetry data was employed to study the adsorption energies and sticking probabilities of D2O and CO2 on CaO(001) at several temperatures. This method deconvolutes the line shapes of the heat detector response into an instrument response function and exponential decay functions, which correspond to the desorption of distinct surface species. This allows for a thorough analysis of the adsorption, dissociation, and desorption processes that occur during our microcalorimetry experiments. Our microcalorimetry results, show that D2O adsorbs initially with an adsorption energy of 85–90 kJ/mol at temperatures ranging from 120 to 300 K, consistent with prior spectroscopic studies that indicate dissociation. This adsorption energy decreases with increasing coverage until either D2O multilayers are formed at low temperatures (120 K) or the surface is saturated (> 150 K). Artificially producing defects on the surface by sputtering prior to dosing D2O sharply increases this adsorption energy, but these defects may be healed after annealing the surface to 1300 K. CO2 adsorbs on CaO(001) with an initial adsorption energy of ~ 125 kJ/mol, and decreases until the saturation coverage is reached, which is a function of surface temperature. The results showed that pre-adsorbed water blocks adsorption sites, lowers the saturation coverage, and lowers the measured adsorption energy of CO2. The calorimetry data further adds to our understanding of D2O and CO2 adsorption on oxide surfaces.

scholarly journals Enhancement of the physical and mechanical properties of wood using a novel organo-montmorillonite/hyperbranched polyacrylate emulsion

Holzforschung ◽  
2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Jianfeng Xu ◽  
Xiaoyan Li ◽  
Ling Long ◽  
Ru Liu
Keyword(s):  
Mechanical Properties ◽  
Cell Wall ◽  
Pinus Radiata ◽  
Wood Sample ◽  
Wood Cell Wall ◽  
Physical And Mechanical Properties ◽  
Radiata Pine ◽  
Compact Structure ◽  
Populus Cathayana ◽  
Modified Wood

AbstractIn this work, a novel waterborne hyperbranched polyacrylate (HBPA) dispersed organo-montmorillonite (OMMT) emulsion was synthesized and used for the treatment of wood in a vacuum environment in order to enhance the physical and mechanical properties of the wood. The sapwood of Cathay poplar (Populus cathayana Rehd.) and Radiata pine (Pinus radiata D.Don) were used as the samples for experimentation. The results showed that the physical and mechanical properties of the wood improved significantly due to the successful penetration of the OMMT and HBPA into the wood cell wall. From it was also observed that OMET completely exfoliated from the HBPA matrix and formed a hydrophobic film covering on the inside walls of the cell lumen. Further, it was observed that the poplar sample displayed better mechanical properties than the pine sample because the pine has a more compact structure when compared to poplar and contains rosin. Furthermore, it was also observed that the mechanical properties of the modified wood sample gradually improved with an increase in the concentration of the emulsion. However, excessive concentration (>4 wt%) did not lead to further improvement.

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