Viscosity of deeply supercooled water and its coupling to molecular diffusion

The viscosity of a liquid measures its resistance to flow, with consequences for hydraulic machinery, locomotion of microorganisms, and flow of blood in vessels and sap in trees. Viscosity increases dramatically upon cooling, until dynamical arrest when a glassy state is reached. Water is a notoriously poor glassformer, and the supercooled liquid crystallizes easily, making the measurement of its viscosity a challenging task. Here we report viscosity of water supercooled close to the limit of homogeneous crystallization. Our values contradict earlier data. A single power law reproduces the 50-fold variation of viscosity up to the boiling point. Our results allow us to test the Stokes–Einstein and Stokes–Einstein–Debye relations that link viscosity, a macroscopic property, to the molecular translational and rotational diffusion, respectively. In molecular glassformers or liquid metals, the violation of the Stokes–Einstein relation signals the onset of spatially heterogeneous dynamics and collective motions. Although the viscosity of water strongly decouples from translational motion, a scaling with rotational motion remains, similar to canonical glassformers.Water, considered as a potential glassformer, has been a long-lasting topic of intense activity. Its possible liquid–glass transition was reported 50 years ago to be in the vicinity of 140?K (1, 2). However, ice nucleation hinders the access to this transition from the liquid side. Bypassing crystallization requires hyperquenching the liquid at tremendous cooling rates, ca. 10⁷?K ? s^?1 (3). As a consequence, many questions about supercooled and glassy water and its glass–liquid transition remain open (4–7).As an example, crystallization of water is accompanied by one of the largest known relative changes in sound velocity, which has been attributed to the relaxation effects of the hydrogen bond network (8, 9). Indeed, whereas the sound velocity is around 1,400 m⋅s−1 in liquid water at 273?K, it reaches around 3,300 m⋅s−1 in ice at 273?K and a similar value in the known amorphous phases of ice at 80?K (10). Such a large jump is usually the signature of a strong glass, i.e., one in which relaxation times or viscosity follow an Arrhenius law upon cooling. However, pioneering measurements on bulk supercooled water by NMR (11) and quasi-elastic neutron scattering (12), as well as recent ones by optical Kerr effect (8, 9), reveal a large super-Arrhenius behavior between 340 and 240?K, similar to what is observed in fragile glassformers (13, 14). The temperature dependence of the relaxation time is well described by a power law (8, 9), as expected from mode-coupling theory (15, 16), which usually applies well to liquids with a small change of sound velocity upon vitrification. Based on these and other observations, it has been hypothesized that supercooled water experiences a fragile-to-strong transition (17). This idea has motivated experimental efforts to measure dynamic properties of supercooled water and has received some indirect support from experiments on nanoconfined water (18–20) and from simulations (21, 22).In usual glassformers, many studies have focused on the coupling or decoupling between the following dynamic quantities: viscosity (η) and self or tracer diffusion coefficients for translation (D_t) and rotation (D_r). If objects as small as molecules were to follow macroscopic hydrodynamics, one would expect that the preceding quantities would be related through the Stokes–Einstein (SE), D_t ∝ T/η, and Stokes–Einstein–Debye (SED), D_r ∝ T/η, relations, where T is the temperature. These relations are indeed obeyed by many liquids at sufficiently high temperature. However, they might break down at low temperature. Pioneering experiments were performed by the groups of Sillescu (23–25) and Ediger (26–28) where a series of molecular glassformers were investigated. SE relation is obeyed at sufficiently high temperature but violated around 1.3T_g, where T_g is the glass transition temperature, thus indicating decoupling between translational diffusion and viscosity. In contrast, it was observed for ortho-terphenyl (23, 24, 26) that rotational diffusion and viscosity remain strongly coupled (i.e., obey the SED relation) even very close to T_g. A corollary is that translational and rotational diffusion decouple from each other at low temperature. These observations imply that deeply supercooled liquids exhibit spatially heterogeneous dynamics (29–31). Dynamic heterogeneities have been confirmed by direct observations of several single fluorescent molecules immersed in ortho-terphenyl (32) or nanorods immersed in glycerol (33). Physically different systems also show analogous behavior. Colloids near the colloidal glass transition violate SE but obey SED (34). In the metallic alloy Zr₆₄Ni₃₆, SE relation is even violated without supercooling, more than 35% above the liquidus temperature (35). This has also been related to the emergence of dynamic heterogeneities (36).For water, SE already breaks down at ambient temperature, which corresponds to around 2.1?T_g (T_g ? 136?K). Molecular dynamics simulations (37–39) have proposed that this occurs concurrently to dynamic heterogeneities caused by a putative liquid–liquid critical point. However, SE and SED also fail by application of high pressure at 400?K (40) where no liquid–liquid transition is expected. To gain more insight, the test of SE and SED in supercooled water deserves further investigation. Translational self-diffusion coefficient D_t (41) and rotational correlation time τ_r (assumed to scale as 1/D_r) (42) have thus been measured down to the homogeneous crystallization temperature (238?K) at ambient pressure. Their comparison reveals a decoupling between rotation and translation that increases with supercooling (42), similar to glassformers. However, viscosity data are needed for a direct test of SE and SED relations. Quite surprisingly, there are only two sets of data for the viscosity η at significant supercooling. Using Poiseuille flow in capillaries, Hallett (43) reached 249.35?K, and Osipov et al. (44) reached 238.15?K. However, the two sets disagree below 251?K, with an 8% difference at 249?K, beyond the reported uncertainties. The measurements in ref. 44 are suspected of errors (45) because of the small capillary diameter used. Here we report η at ambient pressure down to 239.27?K. Our study completes the knowledge of the main dynamic parameters of water down to the homogeneous crystallization limit and allows us to check the coupling of viscosity to molecular translation or rotation, as has been done for usual glassformers.     

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目的探讨血液流变学与复发性口腔溃疡(recurrent oral ulcertion,ROU)发病机制的关系及观察银杏叶提取物(extyact ginkgo biloba,EGb)对ROU血液流变学的影响。方法2004—2005年,在遵义医学院中心实验室用大鼠口腔黏膜匀浆组织加弗氏免疫佐剂注射方法建立大鼠ROU模型,将成功模型动物随机分为阳性对照组、阴性对照组、EGb糊剂组、EGb片剂组、EGb糊剂+片剂组,每组各8只。应用生化分析法和微量毛细管法检测成模前后及用药前后各组大鼠纤维蛋白原、红细胞压积的变化,NEX-2型板式黏度计测定其血浆黏度。结果大鼠成模后的血液纤维蛋白原、红细胞压积、血浆黏度均较成模前增高(P<0.01);治疗后,EGb糊剂组、EGb片剂组、EGb片剂+糊剂组的纤维蛋白原、红细胞压积、血浆黏度均有不同程度的下降,尤其EGb片剂组、EGb片剂+糊剂组更为明显,与对照组比较差异均有统计学意义(P<0.01),而EGb片剂组和EGb片剂+糊剂组之间差异无统计学意义(P>0.05)。结论ROU的发生与微循环障碍有关,EGb能改善ROU模型大鼠的微循环,尤以EGb片剂、EGb糊剂+片剂效果最好。     

Film-forming properties and viscosities of saliva substitutes and human whole saliva

Hypo-salivation, related to medical remedies, is an increasing clinical problem. Studies report a weak correlation between subjective mouth dryness and objective sialometry. This indicates that both quantity and quality of saliva are important for the surface-associated functions of saliva, such as lubrication and hydration, to be expressed. Film-forming properties and viscosities of three saliva substitutes were compared to human saliva. Adsorption to surfaces was measured by ellipsometry, infrared spectroscopy and drop-volume technique. Viscosity measurements were carried out using an oscillating rheometer. Saliva, with the lowest viscosity value and the highest protein content, presented superior film retention on both hydrophilic and hydrophobic surfaces. The carboxymethylcellulose-based MAS 84 showed intermediate values of viscosity, poorest ability to reduce surface tension, and negligible film-forming capacity. The porcine mucin-based Saliva Orthana showed about twice the viscosity of saliva and film-forming capability on preferably hydrophobic substrates. Salinum, a linseed extract, possessed the highest viscosity value and an initial surface tension close to that of saliva. The film retention on hydrophilic surfaces was not as effective as for saliva. The results indicate that the film-forming capacity of saliva substitutes is a property also to be considered in the exploration of clinically effective artificial salivas.     

DTG thermal analyses and viscosity measurements of three commercial agar impression materials

Three commercial agar impression materials, two for clinical uses and one for dental laboratory, were examined for their thermal properties by differential thermogravimetric (DTG) thermal analyses and viscosity measurements. On DTG profiles, an endothermic peak along with weight loss at around 100 degrees C was observed on all three agar impression materials as a result of water evaporation. Two clinical agar impression materials were more susceptible to this trend than the remaining one dental laboratory agar impression material. The viscosity of three agar impression materials could be expressed in the exponential function of temperature. Viscosity at 46 degrees C of one dental laboratory agar impression material far exceeded those of two clinical agar impression materials. Monitoring the viscosity could facilitate the detailed analysis of setting process of agar impression materials upon cooling, and might be useful for future development of agar-based dental impression materials.     

Physical properties and compatibility with dental stones of current alginate impression materials

This study examined physical properties and compatibility with dental stones of two types of alginate impression materials. Five powder-type alginate impression materials (Alginoplast EM, Aroma Fine, Algiace Z, Coe Alginate, Jeltrate Plus) and a paste-type alginate impression material (Tokuso AP-1) were used. The dynamic viscosity immediately after mixing was measured by means of a controlled-stress rheometer. The gelation times were determined according to Japanese Industrial Standards (JIS) T6505, and recovery from deformation, strain in compression and compressive strength were determined according to the International Organization for Standardization (ISO) specification 1563. Detail reproduction and surface roughness of type III dental stones (New Plastone, New Sunstone) and a type IV dental stone (Die Stone) were evaluated using a ruled test block as specified in the ISO specification 1563 and a profilometer, respectively. The alginate impression materials evaluated in this study were all in compliance with the ISO specification 1563 and JIS T6505. The alginate impression materials had similar mechanical properties after gelation, whilst a wide range of dynamic viscosity immediately after being mixed, gelation times and compatibility with dental stones were found among the materials. The paste-type material had a higher dynamic viscosity and a shorter gelation time than the powder-type materials. The best surface quality was obtained with the paste-type material/type III dental stone cast combinations. The materials should be selected in consideration of initial flow, setting characteristics and compatibility with dental stones. The results suggested that a paste-type material would better meet the requirements of an alginate impression material.     

碟脉灵注射液对大鼠实验性心肌梗塞的保护作用及其机制

目的：观察碟脉灵注射液（DMLI）对大鼠实验性心肌梗塞的保护作用及其机制。方法：采用大鼠结扎左冠状动脉前降支造成急性心肌梗塞模型,将动物随机分为假手术组、梗塞模型组及DMLI小、中、大剂量组,每组20只大鼠。计算急性心肌梗塞24 h后的心肌梗塞面积（MIS）,测定血清天冬酸氨基转移酶（AST）、乳酸脱氢酶（LDH）、肌酸磷酸激酶（CK）、超氧化物歧化酶(SOD)、谷胱甘肽过氧化物酶(GSH-Px)活性及丙二醛（MDA）含量,血浆内皮素（ET）及血管紧张素Ⅱ（AngⅡ）水平,观察全血低、中、高切变率黏度及血浆黏度变化,并测定心肌梗塞及非梗塞区游离脂肪酸（FFA）含量。结果：与梗塞模型组比较,DMLI 中、大剂量组急性心肌梗塞24 h大鼠的MIS缩小（P<0.05或P<0.01）,血清AST、LDH、CK活性及MDA降低（P<0.05或P<0.01）, SOD及GSH-Px活性升高（P<0.05或P<0.01）,血液黏度、血浆黏度、血浆ET及AngⅡ水平明显下降（P<0.05或P<0.01）,心肌梗塞及非梗塞区FFA含量降低（P<0.05或P<0.01）。结论：DMLI对大鼠实验性心肌梗塞具有明显保护作用,可能与其增强抗氧化酶活性,减少自由基对心肌的氧化损伤,纠正心肌缺血时FFA代谢紊乱,减少内源性血管活性物质ET及AngⅡ释放以及降低血液黏度等机制有关。     

半夏白术天麻汤治疗后循环缺血性眩晕的系统评价

目的 系统评价半夏白术天麻汤治疗后循环缺血性眩晕的有效性、安全性。方法 计算机检索中国学术期刊全文数据库（CNKI）、万方数据知识服务平台（Wanfang Data）、维普中文期刊全文数据库（VIP）、中国生物医学文献数据库（CBM）、Cochrane Library、PubMed、Embase、Web of Science等数据库,筛选出半夏白术天麻汤治疗后循环缺血性眩晕的随机对照试验（RCT）,检索时限从建库至2023年6月30日。应用Cochrane Handbook 5.1评价文献质量,RevMan 5.3评价软件进行Meta分析。结果 共纳入22项RCTs,包括患者1 763例患者,试验组（半夏白术天麻汤联合化学药治疗或常规治疗） 887例、对照组（单用化学药或常规治疗） 876例。Meta分析结果显示：在提高总有效率方面［OR＝4.10,95% CI（2.95,5.70）,P＜0.000 01］,在改善全血高切黏度方面［SMD＝-0.88,95% CI（-1.30,-0.46）,P＜0.000 1］、改善全血低切黏度方面［SMD＝-1.55,95% CI（-1.84,-1.25）,P＜0.000 01］,在增加基底动脉平均血流流速方面［SMD＝1.32,95% CI （0.85,1.78）,P＜0.000 01］,在增加左/右椎动脉平均血流流速方面［SMD＝2.08,95% CI （1.15,3.00）,P＜0.000 1］/［SMD＝2.04,95% CI （1.10,2.98）,P＜0.000 1］;在改善恶心呕吐症状评分方面［SMD＝ - 4.18,95% CI（-6.14,-2.21）,P＜0.000 1］、头晕目眩症状评分方面［SMD＝-1.13,95% CI（-1.87,-0.40）,P＝0.002］,试验组均优于对照组。研究中明确为不良反应者10例,症状为皮疹或胃肠道不适。结论 半夏白术天麻汤联合化学药治疗或常规治疗,可以明显提高后循环缺血性眩晕的总有效率、改善血流指标、改善恶心呕吐及头晕目眩症状评分,并且不良反应少且轻微,具有安全性及有效性。但由于此次纳入的文献中样本量偏小,需采用更多大样本、设计严谨的临床试验方案提高证据质量级别。     

两种黏度骨水泥对老年重度胸腰段骨质疏松性椎体压缩骨折患者PVP手术效果影响的对比研究

目的比较两种黏度骨水泥对老年重度胸腰段骨质疏松性椎体压缩骨折(OVCF)患者经皮椎体成形术(PVP)手术效果的影响。方法选取2017年5月至2019年4月于我院骨科择期行PVP治疗的老年重度胸腰段OVCF患者152例,利用随机数字表法分成观察组(n=76)及对照组(n=76)。所有对象均行PVP治疗,观察组于PVP术中采取高黏度骨水泥治疗,而对照组采用低黏度骨水泥治疗。汇总两组术后并发症的发生情况;并于术前及术后第1 d和第3、6个月时运用视觉模拟评分法(VAS)评价受试者当时主观疼痛的程度,使用Oswestry功能障碍指数(ODI)评估被调查者运动功能的恢复情况;同时于术前及术后第3、6个月时采用双能X线骨密度仪检测病人腰椎骨密度(BMD)。结果两组疼痛VAS评分均随术后时间的延长而逐渐降低(P0.05),且两组术后第1 d和第3、6个月时疼痛VAS评分均较术前显著下降(P0.05)。两组疼痛VAS评分组间同时间点对比差异均无统计学意义(P0.05)。随术后时间的延长,两组ODI评分均逐渐降低(P0.05);且两组术后第1 d和第3、6个月时ODI评分均显著低于术前(P0.05)。同时观察组术后第3、6个月时ODI评分则均显著低于对照组同期(P0.05)。随术后时间的延长,两组腰椎BMD均逐渐增加(P0.05),且两组术后第3、6个月时腰椎BMD均较术前显著增高(P0.05)。但术后同时间点,两组腰椎BMD比较差异均无统计学意义(P0.05)。两组术后压疮、坠积性肺炎及肺栓塞的发生率对比差异均无统计学意义(P0.05);但观察组术后骨水泥渗漏率[5.26%(4/76)]显著低于对照组[19.74%(15/76),P0.05]。结论与低黏度骨水泥相比,将高黏度骨水泥应用于老年重度胸腰段OVCF病人PVP术中能显著降低患者术后骨水泥渗漏的发生风险。     

红景天联合拜新同治疗糖尿病肾病30例

目的:观察红景天联合拜新同治疗糖尿病肾病的临床疗效。方法:将60例糖尿病肾病患者随机分为对照组和治疗组,每组各30例。对照组给予西医常规治疗,并给予拜新同降血压以降低尿蛋白的排泄,治疗组在对照治疗的基础上联合红景天治疗。观察两组患者治疗前后血压、空腹血糖、糖化血红蛋白(glycosylated hemoglobin,Hb A1C)、24小时蛋白尿、β_2-微球蛋白(β_2-microglobulin,β_2-MG)、肌酐清除率(Creatinine clearance rate,Ccr)。检测两组患者治疗前后血脂水平[三酰甘油(Three acyl glycerol,TG)、总胆固醇(total cholesterol,TC)、低密度脂蛋白(Low density lipoprotein,LDL-C)、高密度脂蛋白(high density lipoprotein,HDL-C)]及血浆纤维蛋白原、全血黏度、全血黏度高切、全血黏度低切等实验室指标变化情况。结果:两组患者治疗后血压、空腹血糖、Hb A1C、24小时蛋白尿、Ccr、TG、TC及LDL-C均低于治疗前,且治疗组低于对照组,差异均有统计学意义(P0.05)。两组患者治疗后β_2-MG、血浆纤维蛋白原、全血黏度、全血黏度高切及全血黏度低切均低于治疗前,差异均有统计学意义(P0.05),但治疗组与对照组比较,差异无统计学意义(P0.05)。结论:红景天联合拜新同治疗糖尿病肾病可改善患者临床症状及实验室指标。     

应用回归方程探讨男性生化指标与血流变关系

目的 本文对男性成年人中常见的生化指标与血液流变学进行了分析，有助于临床医生分析异常生化指标与血液变学之间的关系及疾病的诊断和治疗。方法 以全自动生化分析仪测定血清生化指标，粘度计测量血流变指标，微量毛细管测定红细胞压积（HCT）。结果 根据174例男性人群血液中28项生化指标与11项血流变参数间的关系，建立相应的回归方程，推算它们的关系。结论 血液流变学结果受多种异常生化指标的影响。