土壤持水量 Water holding capacity (WHC) is the ability of a soil to contain and to retain water. Dependent upon the factors, which determine hydraulic conductivity and permeability e.g., texture, organic matter, porosity, interconnectednessof pores and so on. The water is held in the spaces, or pores, between soil particles and in thin films surrounding those particles. It iscalculated by mass of (water contained in the saturated soil / mass of the saturated soil)*100 or water holding capacity (%) = (m (water in saturated soil) / m (saturated soil) ) * 100. Therefore it should be a fixed value during short time. 田间持水量 (Field water capacity) 田间持水量是在地下水位较低(毛管水不与地下水相连接)情况下，土壤所能保持的毛管悬着水的最大量，是植物有效水的上限。田间持水量是衡量土壤保水性能的重要指标，也是进行农田灌溉的重要参数。田间持水量的测定大多采用田间小区灌水法，当土壤排除重力水后，测定的土壤湿度即为田间持水量，其技术操作简介如下： 1 仪器及工具准备 测定前应准备好土壤水分快速测试仪(TSC-1型土壤水分快速测试仪)、土钻(长不小于60cm)、卷尺、草席、塑料布、铁锨、水表或水桶，如果测定地块附近没有水源，还要准备足够的水量等。 2 测定场地的选择 根据我县不同的区域，我们分别选择了代表南部二阴高寒山区的马坡乡、代表北部干旱山区的上花岔乡、代表中部川水地区的清水驿乡3个样地进行测定。 3 测定程序 3.1 测定场地的准备 在所测定的地段上量取面积为4m2(2m×2m)的平坦场地，拔掉杂草，稍加平整，周围做一道较结实的土埂，以便灌水。 3.2 灌水前土壤湿度的测定 在准备好的场地外1～1.50m处，根据应测定田间持水量的深度(0.60m)以内，取2个重复的土样测定土壤湿度，最后求出所有测量值的平均值。 3.3 灌水前土壤湿度的确定 用水分快速测试仪分别对两个重复采样点按0～10cm、10～20cm、20～40cm、40～60cm的4个土层深度进行测量，再取其各层次平均值为该地面测定样方每层的测量值。根据公式 θ0-60cm =(θ0-10cm+θ10-20cm +2θ20-40cm+2θ40-60cm )/6计算得出：马坡乡为17.30%、上花岔乡为8.58%、清水驿乡为10.82%。 3.4 灌水 根据公式Q=2(θ1-θ2 )×S×H／100计算灌水量。其中Q：灌水量，单位m3。θ1 ： 假设的所测深度土层中的平均田间持水量，用体积含水量表示，壤土一般取37.50%，以百分值表示。θ2 ： 灌水前所测深度的各层平均土壤湿度，以百分值表示。S：灌水场地面积，以平方米为单位。H：所要测定的深度，以米为单位。常数2：保证小区需水量的保证系数。经计算，马坡乡灌水量为0.97m3，清水驿乡灌水量为1.39m3，上花岔乡灌水量为1.28m3。 3.5 覆盖 所有水应在1天内分次灌完，为避免水流冲刷表土可先在小区内放一些蒿草(秸秆)或在地埂边放些塑料再灌水。当水分全部下渗后，再覆盖上草席和塑料布，以防止蒸发和降水落到小区内。 3.6 测定时间 灌水后当重力水下渗后，开始用土壤水分快速测试仪测定土壤湿度。壤土在灌水2～3d后开始第1次测定，每天取1次，每次取4个重复，4个重复测点不应靠近小区边缘。 3.7 确定田间持水量 每次测定后，逐层计算同一层前后2次测定的土壤湿度差值，若某层差值≤3%，则第2次测定值即为该层土壤的田间持水量，下次测定时该层土壤湿度可不测定。若同一层次前后2次测定值 ＞3%，则需继续测定，直到出现前后2次测定值之差 ≤3%时为止。在实际操作中， 一定要注意多测量几次，直到前后两次值出现比较稳定为止，不能因为头两三次之差小于3%就确定最后一次值为田间持水量。 空隙含水量 Water filled pore space (WFPS) is also known as degree of saturation; it is the volume of water present in the soil relative to total volume of pores. It is calculated as (percentage ofvolumewater content / percentage of soil pore space) * 100, or WFPS (%) =(percentage ofvolumewater content / percentage of soil pore space) * 100 = (m water / m dry soil ) * soil bulk density / (1 - soil bulk density / soil particle density) * 100. Normally soil particle density is assumed as 2.65 g/cm 3 . 参考: http://bettersoils.soilwater.com.au/module3/3_09.htm ogden_water_holding_capacity_exercise.pdf PDF File.pdf sept 18.pdf SOIL_water_holding_capacity_LAB.doc WFPS.pdf
A friend said he was cheated out of paying for expensive tea leaves. He tasted tea from a big tea-leave bag, liked it, and bought some (from the same bag). After he got home, he made tea himself but it did not taste good. He concluded that he was cheated by the tea farmer. The same thing happened to me, right now; but I came up with a different conclusion. It's not the tea, stupid; it's the water (from the pipes in Beijing) that tastes bad. What do you think?
Twenty-nine percent cited water and air pollution as the most pressing concern, the Washington Post-Stanford University poll indicated, followed by 18 percent who pointed to climate change... http://news.yahoo.com/climate-change-no-longer-tops-us-environment-worries-134721404.html
It's Sunday afternoon in Toulouse, and everyone is out drinking wine or beer. I finally realized why they drink, because I can't find a place that sells water much cheaper than wine/beer! I got a bottle of waterfrom a vending machine for 2 Euro. Maybe I should join them, too! Actually, French smokes a lot, too. Luckily, most hotels in France band smoking now.
日前，2011国家杰出青年基金名单已公示，中国农业大学黄冠华老师名列其中！祝贺！黄老师是我国农业水土工程学科继两位康老师（康绍忠、康跃虎老师）之后为数不多的杰青，进一步提升了农大在农水方向的地位。黄老师主要研究方向为农业水土环境，现在正在致力于建设农水与水文水资源交叉的学科方向“农业水土资源与环境”。近年来已在国际主流期刊发表了一系列成果，据检索，在Water Resources Research、Journal of Hydrology、Advance in water Resources、Agricultural Water Management发表的文章位于中国大陆研究学者前列。
Report “Confronting the Global Water Crisis through Research” Uncovers Key Trends in Water Resources Research Global water research grows nearly 30 percent annually during past decade Amsterdam, March 22 nd , 2011 – The report “Confronting the Global Water Crisis through Research – 2010”, carried out by Elsevier and released today, reveals the increasingly international and strategic nature of water resources research. Examining major trends in water research at the international, national and institutional levels, the report highlights the escalation in the article output of countries conducting water resources research and the expansion of such research into strategic disciplines. Elsevier used Scopus data and one of the solutions from its performance and planning suite, SciVal Spotlight, to develop a detailed analysis of country and institutional strengths in the field. “Most countries realize the importance of multidisciplinary research in water research as they face climate change and population growth,” said Dr. Christiane Barranguet, Executive Publisher of Elsevier Aquatic Sciences. “This is reflected by the nearly 30% annual growth rate in global water resources research from 2000 to 2009, as countries increasingly look to science to find answers to pressing questions regarding local and global water resources demands.” Key findings from the report include: • The Emergence of China While the U.S. leads in producing water resources research and yields the widest variety of such research, China is quickly emerging as a key player in the field. From 2003 to 2010, the number of articles published on water resources research from institutions in China increased by 28% annually while the number of articles published by U.S. institutions increased at a rate of 11%. If a straight-line growth trend is assumed, China will surpass the U.S. in the number of articles published on water resources research in 2014. • International Growth Given the strengths of its research and grant-making institutions, the U.S. will likely maintain a leading role in water resources research. However, the international focus on water resources suggests that the U.S. will increasingly share the research stage with other countries. The data indicates a rapid growth of water resources research throughout the world, including some countries where until recently, there was very little of such research. Faced with economic expansion, rising populations and growing industrialization, countries such as Iran, India, Russia, South Africa, Brazil and Mexico have experienced severe water problems and have subsequently seen dynamic increases in water research. For example, Iran produced only 12 papers on water resources between 1970 and 2000, but produced more than 60 papers each year from 2005 to 2008. • Multidisciplinary Growth By extensively mapping research articles by discipline, data from SciVal Spotlight reflects the increasingly multidisciplinary nature of water resources research. While environmental sciences, earth sciences, engineering and biological sciences continue to dominate the field, disciplines such as economics, math, computer science, chemistry and biochemistry are rapidly expanding into water research. Economics in particular, has seen significant growth. From 2004 to 2008, the annual growth rate in economics articles within water resources research was 100%. The rise of these disciplines highlights the changing interests of governments and grant-making institutions as they work to solve a variety of problems associated with water resources. To receive a copy of the report, please contact Sandra Plasse at +1 212-752-8338 or splasse@psbpr.com . # # # Survey Methodology The analysis was split in to two phases: phase I looked at the water resources literature landscape and phase II, which took a look at a number of well performing nations and one of their institutions that is a main contributor to the subject field. Phase I - To construct the initial data pool, the keywords "water resources*" were used to search titles, abstracts, and keywords of original articles, reviews, and proceedings papers published in the SciVerse Scopus™ database (http://www.info.sciverse.com) from Elsevier between January 1, 2004 and Dec 31, 2008. The resulting pool of research papers related to water resources was then analyzed. The data pool was used to generate list of subject categories, institutions, and nations ranked in three ways: according to total number of papers, total cites, and total cites/paper. Phase II - SciVal® Spotlight (http://www.info.scival.com/) was used to gain deeper insights into the core strengths of these top nations and the institutions that are contributing to these national strengths. About the Elsevier SciVal ® Suite Elsevier’s SciVal suite ( http://www.info.scival.com ) of services supports academic and government leadership in evaluating, establishing and executing research strategies that optimize the performance of existing assets and maximize investments to enhance near and long-term productivity. SciVal tools leverage Scopus® data, Elsevier’s trusted source of bibliometric data, to offer innovative yet authoritative solutions. Current suite offerings include: SciVal Spotlight™, a strategic tool that generates unique institutional and country maps of existing and emerging strengths based on an interdisciplinary perspective of current performance; SciVal Funding™, an online solution that provides targeted recommendations on grants to pursue based on pre-populated research profiles and historical awards; SciVal Experts, a semantic technology-based application that enables researchers to identify and locate sources of expertise at an individual or departmental level within and across institutions. About Elsevier Elsevier is a world-leading publisher of scientific, technical and medical information products and services. The company works in partnership with the global science and health communities to publish more than 2,000 journals, including The Lancet and Cell , and close to 20,000 book titles, including major reference works from Mosby and Saunders. Elsevier’s online solutions include SciVerse ScienceDirect , SciVerse Scopus , Reaxys , MD Consult and Nursing Consult , which enhance the productivity of science and health professionals, and the SciVal suite and MEDai’s Pinpoint Review , which help research and health care institutions deliver better outcomes more cost-effectively. A global business headquartered in Amsterdam, Elsevier employs 7,000 people worldwide. The company is part of Reed Elsevier Group PLC , a world-leading publisher and information provider, which is jointly owned by Reed Elsevier PLC and Reed Elsevier NV. The ticker symbols are REN (Euronext Amsterdam), REL (London Stock Exchange), RUK and ENL (New York Stock Exchange). Media Contacts Sandra Plasse/Jen Saunders +1 212-752-8338 splasse@psbpr.com jsaunders@psbpr.com
Although some tests continue, state and federal health officials say the tiny amounts found in milk so far are not dangerous By William Cole State health officials are testing large rainwater catchment systems this week on the Big Island, Maui and Kauai for radiation from Japan's nuclear release, but re-emphasized that radiation in milk, rainwater and likely in locally grown produce remains minute. Lynn Nakasone, administrator of the Health Department's Environmental Health Services Division, said produce will not be tested, as other officials noted there is concern about creating a health scare and hurting local farmers. "I know people are thinking, ‘Oh, a little bit (of radiation) here, a little bit there (adds up),' " Nakasone said. "But think of it as calories. What if milk had 0.000004 calories and produce had 0.000003 calories and so on? So you add up all these little calories, but then you probably won't get to even one calorie. "(The radiation from Japan) is kind of like that. We're talking about so minute amounts. Even if you took all the cumulative doses for everything, you are still way below any kind of action level and it's not a health risk at all." http://www.staradvertiser.com/news/hawaiinews/20110419_radiation_no_problem.html
很有意思，为一个病原写一首歌，这个微生物曾经震动美国朝野。 Title:Cryptosporidium Septicemia, Yersinia Pestis Delusional Hyponatremia H2O poisoning without knowing Tap water infects my throat Nausea, retching, pallor bowel movements Epigastric discomfort Consume water from the sink Trying to rehydrate myself Virulent liquid maggots produce Rapid progressive condition Instant depletion of body fluids Electrolyte balance precarious Secretion of intestinal polypeptide Dilation of blood vessels Asiatic cholera secreting fluid and salt In the intestinal tract, viremia, vipoma, Water born epidemic Confusion in thought Intestinal rot, Bacterial Fate Trying to rehydrate Leading to hypovolemia... chronic renal dysfunction Massive loss of potassium, ion (K) from diarrhea and vomiting, Reaching for the stash tray Load a bowl... fire it up Trying to control nausea Internal anal hemorrhaging, bleeding sphincter and constantly wiping, Lying in pain slowly dying Wandering in disbelief Yearning at the terror inside me Cramping in unbearable I want to cry Somehow this has to end Same bacteria eats my friends Drink Pepto-Bismal to remiss Smoke a joint to progress Pale and pink... acid vomit sprays Dizziness erupts... I slip away Immune system starts to fade A fight with time Antibiotics will save my life Cryptosporidium killing inside Burning and churning, intestines writhe I am still breathing, but barely alive Parasites dying, I come back to life Cheating death, smoke another bowl Regaining hope, bless my soul The body is gaining strength No more bloody stool, I hit the bong Eating to constipate Hoping I won't defecate Water epidemic deploys town A defective filter is what was found At the water treatment plant, Intake/Outtake valves Were somehow crossed, sending untreated sewage Into the home, community infected... Cryptosporidium infecting my body, Living to tell the this purulent story Smoking some kind and feeling alive
http://www.flowthefilm.com/trailer About the Film Irena Salina's award-winning documentary investigation into what experts label the most important political and environmental issue of the 21st Century - The World Water Crisis. Salina builds a case against the growing privatization of the world's dwindling fresh water supply with an unflinching focus on politics, pollution, human rights, and the emergence of a domineering world water cartel. Interviews with scientists and activists intelligently reveal the rapidly building crisis, at both the global and human scale, and the film introduces many of the governmental and corporate culprits behind the water grab, while begging the question "CAN ANYONE REALLY OWN WATER?" Beyond identifying the problem, FLOW also gives viewers a look at the people and institutions providing practical solutions to the water crisis and those developing new technologies, which are fast becoming blueprints for a successful global and economic turnaround. On December 10th, 2008 FLOW was invited to screen at the United Nations as part of the 60th Anniversary of the Declaration of Human Rights. Watch the video here: FLOW at the UN
水循环过程中，除了自然力驱动的水的自然水循环，还包括社会力所驱动的社会水循环。在社会水循环过程中，内在驱动力是水的经济社会效益，而外在的物化表现则是电力驱动的水泵。 Vast amounts of energy are needed for the transportation, distribution and treatment of water. Pumping it over mountain ranges or from deep underground aquifers also requires a significant amount of energy. But the largest share of energy use comes from individual customers who heat water to bathe, cook and run businesses. 研究结果正如上面所说， 能源消耗最大的位于用水终端的个体水消费者。 Results： （1）In the sector of water extraction and delivery, only 23% of electricity requirements are used for water pumping out, purification, and distribution. Energy costs varydepending on the pumping distance, water quality, water pipelines, and water source. Groundwater pumping can increase energy use 30% over surface water sources. (2) End use: In this sector, up to 73% electricity requirements are needed in water cycle by homes, farms, and businesses. It is reported that household appliance such as washing machine, dishwasher, water heaters, and dryers use the largest amount of electricity in water cycle, 28%. (3) Waste water management just costs only 4% energy, which not only reveals waste treatment currently need less energy but shows there is lot of potentiality we can clean much moredischargedwater again. So far, only 4% electricity was used for water cleaning before it is discharged to water source. However, with the population growth and increasingly stringent treatment standards, more and more energy is needed, which could soon lead to increased wastewater management costs. Discussion Based on the results above, I suggest we should shift our eyes from water to energy and water together. How to do some comprehensive research on water cycle driven by energy requirements should be the focus of water cycle research in the future.
Hydrogen is one of the most pervasive elements in the crust and upper mantle of our planet. It is a mobile, reactive component which can cause major changes in the chemical, physical, rheological, and electronic properties of the host phase. Much of the effort of our group is directed at investigating the possibility that hydrogen, in some chemical form (typically OH - and H 2 O), can enter the structure of major minerals which are usually formulated as anhydrous. These studies rely heavily upon spectroscopic methods of analysis because they can determine both the chemical species present and, with proper calibration, the amount of hydrogen present. Both water molecules and hydroxide groups are found in a variety of minerals. Initial studies focused on water in quartz because of its weakening effect upon the mechanical strength of this mineral. We showed that while OH groups have no effect upon the strength of quartz, the amount of water present as clusters of a few water molecules was directly associated with mechanical weakening. Hydroxide groups have subsequently been found in plagioclase feldspars, garnets, sillimanite and other aluminosilicates, olivines, clinopyroxenes, orthopyroxenes, quartz, rutile and zircon. Water molecules occur in nepheline, potassium feldspar, cordierite and other ring silicates. These molecules and ions are structurally bound in the mineral in definite sites with distinct orientations. They often persist in the minerals even at elevated temperatures (up to 1200C). The hydrogarnet substitution (SiO 4 = H 4 O 4 ) has commonly been assumed to represent the mechanism of entry of OH into silicates. Consequently, we are particularly interested in characterizing hydrous components in garnets. We have examined hundreds of garnets of diverse composition and occurrence but rarely find one which is devoid of bound OH. When present in garnets at high concentration (more than 0.5% wt ), hydrogen is in the hydrogarnet substitution. When present at low concentration, infrared and nuclear magnetic resonance spectroscopic data suggest a variety of other incorporation mechanisms. In some silicate minerals, the incorporation of hydrogen is coupled with other light elements such as boron. Much of our interest in hydrous components has focused on the volatile reservoirs and inventories in the upper mantle. We have identified distinctly measurable and petrologically significant quantities of OH in a variety of mantle minerals. Olivine, pyrope, clinopyroxene, rutile, kyanite, and zircon from diamond pipes and other upper mantle sources are among the most OH-rich examples of these particular species. Pyrope garnets, in particular, reflect the buildup of water in their differentiating parent magmas. The thesis of a recent graduate, David Bell, showed that the garnet megacrysts from kimberlites are more hydrous than compositionally equivalent garnets from alkali basalts, eclogitic paragenesis or from inclusions in diamonds. The typical OH concentrations of garnets from southern African mantle samples are significantly lower than those from the mantle of the Colorado Plateau. This observation re-enforces suggestions of significant large-scale regional mantle heterogeneity. We also characterized sub-micrometer inclusions in turbid diamonds which represent samples of fluids trapped in the upper mantle. The high content of H 2 O, CO 2 , carbonate, and enrichment in K, Na, P, Ti, and incompatible trace elements in these inclusions suggest that these fluids are a metasomatizing agent in the mantle.
Ultrafast vibrational dynamics of interfacial water Avishek Ghosh a, Marc Smits a, Maria Sovago a, Jens Bredenbeck a,1, Michiel Mu ller b, Mischa Bonn a,* Chemical Physics 350 (2008) 2330 摘要 We report investigations of the vibrational dynamics of water molecules at the waterair and at the waterlipid interface. Following vibrational excitation with an intense femtosecond infrared pulse resonant with the OH stretch vibration of water, we follow the subsequent relaxation processes using the surface-specific spectroscopic technique of sum frequency generation. This allows us to selectively follow the vibrational relaxation of the approximately one monolayer of water molecules at the interface. Although the surface vibrational spectra of water at the interface with air and lipids are very similar, we find dramatic variations in both the rates and mechanisms of vibrational relaxation. For water at the waterair interface, very rapid exchange of vibrational energy occurs with water molecules in the bulk, and this intermolecular energy transfer process dominates the response. For membrane-bound water at the lipid interface, intermolecular energy transfer is suppressed, and intramolecular relaxation dominates. The difference in relaxation mechanism can be understood from differences in the local environments experienced by the interfacial water molecules in the two different systems. 正文 本文作者利用IR pump VSFG Probe的方法研究了waterair和waterlipid界面水分子的OH伸缩振动的弛豫动力学。实验技术是通过add to the VSFG scheme an additional 'pump', or excitation, pulse, which excites a significant fraction of OH groups to their first vibrationally excited state 。 The femtosecond time-resolved SFG study presented here allows to selectively probe the lifetime dynamics (T1) of the OH stretch vibration and provides new insights in the structure and dynamics of interfacial water. Comparing the waterair interface and the waterlipid interface , pronounced differences of the mechanism and timescale of interfacial vibrational energy flow are found. 实验结果发现，waterair界面的水分子振动弛豫中有两个timescales而waterlipid界面水分子只有一个timescales。所以waterair界面的水分子的弛豫动力学中包含了一个中间态，而waterlipid界面水分子则是不包含中间态的一个单指数的过程。 For the waterair interface (Fig. 3A), two timescales seem apparent: a fast (200 fs) relaxation time corresponding to the recovery of the pump-induced bleach signal (most clearly evident at m = 3500 cm1, and a slower (500 fs) timescale by which the final SFG level is reached (most apparent at m = 3200 cm1). Such dynamics are reminiscent of previous observations for bulk water and observations for water at the waterquartz interface . Hence, it is clear that the hydrogen-bonded network vibrational dynamics at the waterair interface are dominated by ultrafast vibrational energy transfer processes. This also explains the similarity between the dynamics at the waterair interface and those at the hydrophilic and hydrophobic silica/water interface recently reported using SFG in total internal reflection (TIR) geometry . For the latter interface, McGuire and Shen reported somewhat slower dynamics, with T1 = 300 fs and Tthermalization = 700 fs. The rigid silica surface (required for TIR-SFG) has been shown to induce order in the interfacial water compared to water at the waterair interface . The effect of the increased order on the vibrational dynamics is limited due to the ultrafast energy transfer processes that dominate the observed relaxation behavior. Remarkably, Fig. 3B reveals that the behavior of water at the waterlipid interface is very different from that at the waterair interface. Unlike the waterair interface, the data can be described very well by a single exponential decay, with distinct time constants at different probe frequencies within the hydrogen-bonded regime. Reference: J.A. McGuire, Y.R. Shen, Science 313 (2006) 1945. M. Smits, A. Ghosh, M. Sterrer, M. Muller, M. Bonn, Phys. Rev. Lett. 98 (2007) 4. A. Ghosh, M. Smits, J. Bredenbeck, M. Muller, M. Bonn, J. Am. Chem. Soc. 129 (2007) 9608.
Is the liquid water surface basic or acidic? Macroscopic vs. molecular-scale investigations 摘要 Many physical phenomena are affected by the intrinsic acidity/basicity of the free liquid water surface, yet it remains an active and controversial subject. Macroscopic bubble and droplet experiments have been interpreted to indicate an airwater interface covered with hydroxide, whereas recent molecularscale studies produce the opposite conclusion, viz. that hydroxide is repelled from the interface while hydronium is strongly adsorbed. Here we report results from resonant UV second harmonic generation (SHG) experiments that are best modeled by surface depletion of hydroxide and establish at most a weak surface adsorption. This finding is consistent with our earlier SHG measurements indicating surface enhancement of hydrated protons, as well as with other molecular-scale experiments and simulations, but stands in stark contrast to the results from macroscopic studies. The acidity, or basicity, of aqueous surfaces could strongly influence heterogeneous atmospheric chemical processes, such as aerosol reactions and gas uptake. SHG方法能够从微观的角度研究界面离子浓度，他们研究组之前的UV SHG研究空气水界面的工作中发现了hydrated protons在表面的富集。但是这和一些宏观研究方法的结果似乎有些矛盾。UV SHG可以直接和溶液中的CTTS共振，Hydroxide exhibits a broad charge-transfer-to-solvent (CTTS) transition centered at 187 nm in the bulk ，从而可以研究溶液界面的离子，We have taken a different approach and applied SHG in the UV to directly probe the interfacial ions. At the UV wavelengths used in these experiments, water possesses no resonances, whereas several anions exhibit strong charge-transfer-to-solvent (CTTS) transitions . 本文题目是水的界面是酸性还是碱性？ At 225 nm, the SHG intensity remains constant, within experimental uncertainty, due to the limited concentration range explored. At 200 nm, however, the SHG intensity increases significantly at high bulk concentration. Since such a bulk concentration-dependence increase is not observed at the non-resonant wavelengths, this constitutes a direct measurement of surface hydroxide ions at these high concentrations. However, this does not in itself imply surface enhancement of hydroxide. As described above, a small fraction of hydroxide will always exist at the interface despite a repulsive Gibbs free energy due to thermal fluctuations. 讨论 Our direct experimental support for weak hydroxide and strong hydronium propensities for the water surface agrees with the other molecular-level investigations, as described above, but are in stark contrast to the interpretations of macroscopic bubble and droplet electrophoresis experiments . Those experiments measure the motion of gas bubbles or oil droplets in aqueous solution when an electric field is applied. The motion of the droplets/bubbles is analyzed in terms of their zeta-potential and is interpreted as a measure of the overall charge of the droplet/bubble. For neutral and basic pH, the derived zeta-potential is negative, implying that the droplets and bubbles carry a negative surface charge, and only at low pH is a positive zeta-potential observed, i.e. the isoelectric point is around pH 34. Such findings appear universal for hydrophobic interfaces and have been interpreted as clear evidence for a strong surface enhancement of hydroxide . However, those experiments only show that the bubbles and droplets behave as though they are negatively charged, moving in a solvent bath that would have to be positively charged, and not directly establishing that the outermost liquid layer is covered by hydroxide.
标签: Water
