共查询到19条相似文献,搜索用时 78 毫秒
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利用差示扫描量热仪(Pyrid-Diamond DSC),研究乙二醇(EG)和丙三醇水溶液加入0.1%、0.5%质量分数,20nm、40nm、60nm粒径的HA纳米微粒后的过冷度、水合性质,分析HA纳米微粒对线性多元醇水溶液这些特性的影响。实验表明,纳米微粒加入后,线性多元醇水溶液过冷度显著降低,并随纳米微粒粒径增大而减小。水合实验的结果表明,HA纳米微粒对多元醇水溶液的水合性质影响显著,与未加入HA纳米微粒的线性多元醇溶液相比,纳米低温保护剂结晶焓降低,结合水含量增大。 相似文献
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抑制共晶产生对低温保存非常重要。本文利用差示扫描量热法研究了加低温保护剂(DMSO、乙二醇、 1,2丙二醇、甘油和1,3丁二醇)的NaCl水溶液的共晶行为。得到以5%、10%、15%NaCl水溶液为母液的五种保护剂溶液热流曲线图。研究发现,溶液共晶是过冷、随机过程。低温保护剂有抑制NaCl水溶液共晶的作用。低温保护剂浓度越高, 共晶焓越小,对共晶的抑制作用越大。不同种类保护剂的抑制共晶的能力从强到弱依次是甘油、乙二醇、 DMSO、 1,2 丙二醇和1,3丁二醇。升温过程中,溶液发生共晶反玻璃化现象和玻璃化现象。 相似文献
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Marangoni珠状凝结液珠半径分布的研究 总被引:1,自引:0,他引:1
以水-酒精混合蒸汽在斜块上的Marangoni凝结实验图片为基础,统计分析了不同浓度和过冷度下凝结液珠的半径数目比例分布、平均半径及半径偏差.研究发现:在不同浓度和过冷度下,凝结液珠的半径大部分集中在0.1 mm~0.3 mm半径范围内,占到液滴总数的80%;凝结液珠平均半径随过冷度的增大而增大,随浓度的增大而减小;半... 相似文献
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本文从(R)-(-)-1,3-丁二醇 ((R)-(-)-1,3-Butanediol) 的拉曼峰强和拉曼旋光峰强, 求得其键极化率和微分键极化率, 得出在拉曼过程中, 电荷主要沿H16 (或H15) O6C3C2C1O5所形成的 (六边) 环向外围的OH键和CH 键流动. 而此环内外化学键的微分键极化率的符号正好相反, 此意味着这个分子具有相当好的手性不对称性质.
关键词:
旋光拉曼
键极化率
微分键极化率
1,3-丁二醇 相似文献
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Specimens of six enchytraeid species from a wide range of terrestrial habitats were cooled to -25 degree C and rewarmed at 1 degree C/min and their cryobiological features measured by DSC. All were freezing intolerant, supercooling on average to c.-9 degree C. The quantity of frozen (osmotically active) water, calculated from the melt endotherm, varied considerably from 17 to 62% depending on the species and formed three groups. It is suggested that variation in the amount of water frozen in the worms reflects the acclimatisation of these species to the environmental conditions of their habitats. 相似文献
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Li-Ping Wang 《中国物理 B》2021,30(6):68203-068203
Understanding the behaviours of ice nucleation in non-isothermal conditions is of great importance for the preparation and retention of supercooled water. Here ice nucleation in supercooled water under temperature gradients is analyzed thermodynamically based on classical nucleation theory (CNT). Given that the free energy barrier for nucleation is dependent on temperature, different from a uniform temperature usually used in CNT, an assumption of linear temperature distribution in the ice nucleus was made and taken into consideration in analysis. The critical radius of the ice nucleus for nucleation and the corresponding nucleation model in the presence of a temperature gradient were obtained. It is observed that the critical radius is determined not only by the degree of supercooling, the only dependence in CNT, but also by the temperature gradient and even the Young's contact angle. Effects of temperature gradient on the change in free energy, critical radius, nucleation barrier and nucleation rate with different contact angles and degrees of supercooling are illustrated successively. The results show that a temperature gradient will increase the nucleation barrier and decrease the nucleation rate, particularly in the cases of large contact angle and low degree of supercooling. In addition, there is a critical temperature gradient for a given degree of supercooling and contact angle, at the higher of which the nucleation can be suppressed completely. 相似文献
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Nedved O 《Cryo letters》2000,21(1):25-30
The tropical beetle Stenotarsus rotundus (Endomychidae) survived chilling at mildly low temperatures (above +5 degree C). With upper limit of cold injury zone (ULCIZ, the highest temperature that causes cold injury) well above freezing point, the supercooling ability (mean supercooling point - SCP; -11 degree C) has no cryoprotective importance. Mortality increases rapidly between -9 and +5 degree C, dependent on accumulated dose of chilling (sum of injurious temperatures - SIT; 2 degree-days below ULCIZ). The cold hardiness traits found in this species are by-products of deep diapause, and may serve as pre-adaptation for expansion into cooler regions. 相似文献
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Using molecular dynamics, we investigate the crystal nucleation in a Lennard-Jones fluid as a function of the degree of supercooling. At moderate supercooling, a nucleation picture applies, while for deeper quenches, the phenomenon progressively acquires a spinodal character. We show that in the nucleation regime, the freezing is a two-step process. The formation of the critical nucleus is indeed preceded by the abrupt formation of a precritical crystallite from a density fluctuation in the fluid. In contrast, as the degree of supercooling is increased, crystallization proceeds in a more continuous and collective fashion and becomes more spatially diffuse, indicating that the liquid is unstable and crystallizes by a spinodal mechanism. 相似文献
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Free-living microbivorous nematodes become numerically dominant in Antarctic terrestrial faunas as environmental conditions become more severe, while also reaching very high levels of abundance in moist, vegetated habitats. Nematodes have little resistance to freezing via exogenous ice nucleation, such as would occur as their microhabitat freezes. We report the results of experiments testing the ability of seven maritime Antarctic nematode taxa to survive freezing in small water droplets at high sub-zero temperatures. Isolated individuals of these species possessed supercooling characteristics similar to those previously reported (supercooling points -6 to -25 degree C). When frozen in water at -3 to -6 degree C, most showed high (> 70%) survival both (i) after rapid cooling (1 degree C/min) to c. -60 degree C followed by immediate rewarming, and (ii) when held for 7-12 h at either -10 or -30 degree C, although the proportions surviving varied between species. We propose that the ability to survive freezing while fully hydrated at high sub-zero temperatures is one of the most important aspects of these species' survival tactics. 相似文献
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Michael Di Gioacchino Fabio Bruni Armida Sodo Silvia Imberti 《Molecular physics》2019,117(22):3311-3319
Neutron diffraction with isotopic H/D substitution on water, augmented by Empirical Potential Structure Refinement has been applied to extract the hydration properties of the osmolyte zwitterionic ectoine at 1.5?M concentration. This has evidenced differences between the hydration of COO? and NH groups, both in terms of number of water molecules involved in the hydration shell and of three-dimensional symmetry. Signatures of ectoine–ectoine contacts, due to hydrogen bonds, have been found, as possible precursors of ectoine aggregation at higher concentrations. The influence of ectoine on the water structure is ascribed to the dipolar electric field generated by the exposed charges of ectoine. 相似文献
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M. Y. Hassaan 《Hyperfine Interactions》1988,42(1-4):1199-1202
Portland cement was prepared by adding 1,3,5 and 6 wt% gypsum to Egyptian clinker. Each sample was mixed with 25wt% water and was hydrated at 1,3,7,28 and 90 days. The Mössbauer spectra showed two doublets, one represents the tetrahedral ferric ions and the other the octahedral ferric ions in addition to the iron metal. The degree of hydration was calculated from the spectra. The compressive strength test was performed. The time at which complete hydration takes place and the corresponding value of compressive strength were expected by calculations. The 5wt% sample showed the highest value of strength at the same degree of hydration. It showed also the lowest degree of hydration at the same value of compressive strength. It could be concluded that the optimum amount of gypsum addition should be 5 wt%, and the rate of hydration didn't affect by the different amount of gypsum. 相似文献