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151.
Polymer films have been known to change their physical properties when film thickness is decreased below a certain value.
The cause of this phenomenon is still unclear but it has been suggested that interactions and/or chain free-volume changes
at the surface of the films are largely responsible for this behavior. In this paper, the effect of substrate interactions
on the behavior of polymer thin films is evaluated quantitatively. The infrared spectra of nanothin polyethylene (PE) films
were recorded as a function of temperature and amount of substrate covering the surface of the film. The evolution of specific
bands in the CH2 rocking region of the spectra was used to determine the melting temperature (T
m
) of the material. Results show different variations in T
m
depending on the nature of the substrate, indicating that interactions dominate free-volume considerations in PE thin films.
By varying the amount of surface coverage, a quantitative estimate of the heat of interaction was determined, which confirmed
the importance of surface interactions. 相似文献
152.
用标准的固相反应法制备了La0.3Ca0.7Mn1-xWxO3(0.00≤X≤0.15)多晶样品.通过对样品磁化强度-温度(M-T)曲线、磁化强度-磁场强度(MH)曲线及ESR谱的测量,研究了Mn位W掺杂对La0.3Ca0.7Mn1-xWxO3体系的磁相变的影响.结果表明,随着W掺杂量的增加,体系磁相变发生了复杂的变化过程.当掺杂量为0.00≤X≤0.08时,体系存在电荷有序(CO)相,反铁磁(AFM)/C0态共存于相变温度以下,电荷有序温度(Tco)随着W掺杂量的增加而增加.x≥0.12时,体系电荷有序态逐渐减弱并融化,在极低温度下存在顺磁-铁磁(PM-FM)相变. 相似文献
153.
以1,4-丁二醇为引发剂、辛酸亚锡为催化剂,通过L-丙交酯(LLA)、乙交酯(GA)、ε-己内酯(CL)的开环共聚,制得了低分子量的端羟基结晶性LLA/GA共聚物(PLLGA)和CL/GA共聚物(PCG),分别以FTIR1、H-NMR、GPC、DSC对其微结构和热转变温度进行了表征,重点考察了其热转变温度的组成、分子量依赖性.结果表明,利用辛酸亚锡/二元醇引发开环聚合,通过改变单体配比和单体/引发剂配比,可方便地调控共聚物的组成和分子量;通过改变共聚物的组成和分子量,可在较宽的范围内调节共聚物的热转变温度,并得到了玻璃化温度和熔点与组成、分子量之间定量的经验关系式. 相似文献
154.
Differential scanning calorimetry (DSC) has been widely applied to study crystallization and melting of materials.However,for polymeric lamellar crystals,the melting thermogram during heating process usually exhibits a broad endothermic peak or even multiple endotherms,which may result from changes of metastability via recrystallization process.Sometimes,the recrystallization exotherm cannot be observed due to its overlapping with the melting endotherm.In this work,we employed a step heating procedure consisting of successive heating and temperature holding stages to measure the metastability of isothermally crystallized poly(butylene succinate) (PBS) crystals.With this approach we could gain the fraction of crystals melted at different temperature ranges and quantitatively detect the melting-recrystallization behavior.The melting-recrystallization behavior depends on the polymer chain structure and the crystallization temperature.For instance,PBS block copolymer hardly shows recrystallization behavior while PBS oligomer and high molecular weight PBS homopolymer demonstrate remarkable melting-recrystallization phenomenon.High molecular weight PBS isothermally crystallized in the low temperature range shows multiple melting-recrystallization while those isothermally crystallized at elevated temperatures do not exhibit observable recrystallization behavior.Furthermore,the melting endotherms were fitted via the melting kinetics equations.The original isothermally crystallized lamellae demonstrate quite different melting kinetics from the recrystallized lamellar crystals that melt at the highest temperature range,which is attributed to the different degrees of stabilization.Finally,the mechanism of melting-recrystallization is briefly discussed.We propose that apparent meltrecrystallization phenomenon be observed when melting of preformed lamellar crystals and recrystallization of thicker lamellae have similar free energy barrier. 相似文献
155.
Standard methods of thermodynamics are used to investigate fluctuation conditions for individual nanoparticles. This analysis
leads to a theorem on fluctuations of nanoparticles in the vicinity of the phase transformation temperature stating that fluctuations
are possible only between an equilibrium and a non-equilibrium phase. The basic conditions used to describe fluctuations are
well suited to calculate the limits for fluctuations as function of temperature and particle size. 相似文献
156.
D. Partouche-Sebban D.B. Holtkamp J.L. Pélissier J. Taboury A. Rouyer 《Shock Waves》2002,11(5):385-392
Temperature is a basic parameter in physics, but in the case of shock-compressed metals its measurement remains difficult
and controversial. Improvements in accuracy of a high-speed optical pyrometer enabled us to study interesting features of
bismuth: temperatures of shock-loaded samples measured through a lithium-fluoride anvil and (indirectly) part of the fusion
curve. An improved method of analyzing optical pyrometry data is also discussed.
Received 10 June 2001 / Accepted 31 October 2001 相似文献
157.
银原子团簇在纳米碳管中的形态与熔化特性 总被引:2,自引:1,他引:1
沈海军 《原子与分子物理学报》2005,22(4):676-680
采用分子动力学方法,对纳米碳管中Agn(n=108,402)团簇的形态及熔化特性进行了模拟,并与自由状态下团簇的形态及熔化特性进行了对比。研究表明,①温度T=150 K时,碳管中银团簇的形态呈现为吸附在碳管内侧的单原子层银管,表现为非晶体,而自由状态下的银团簇呈现为近似球形,且具有一定的晶体特征。②自由状态下银团簇的熔化为“晶体熔化”,而纳米碳管中的银团簇为非晶熔化。 相似文献
158.
Three ionic liquids with borate anions of low symmetry, tetraethylammonium difluoromono[1,2-oxalato(2-)-O,O′]borate, 1-ethyl-3-methylimidazolium difluoromono[1,2-oxalato(2-)-O,O′]borate, and 1-butyl-3-methylimidazolium difluoromono[1,2-oxalato(2-)-O,O′]borate were synthesised and characterised by physicochemical and electrochemical measurements including thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), cyclic voltammetry (CV), viscosity and conductivity measurements. 相似文献
159.
160.