Advances in Colloid and Interface Science-猫眼课题宝

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2010

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G. J. Fleer

Gerard Fleer“Daar heb je een goeie aan”用这句简短的荷兰语句子TheoOverbeek向Hans Lyklema推荐并描述了Gerard，他开始在瓦赫宁根大学攻读博士学位。这句话很难翻译，但意思是“Thereyou have a top notch man”。Overbeek的高期望被年轻学生随后的职业生涯所证明，现在，四十年后，很明显，杰拉德没有辜负人们的期望。所以，我们有充分的理由在《胶体与界面科学进展》的特刊上表彰他。奥弗贝克对他这位有前途的学生的良好评价，部分是基于杰拉德在乌得勒支大学化学和物理领域的优异成绩，部分是基于他的个人判断。杰拉德通过了大学的最后一次考试（当时称为“博士考试”，比现在的理学硕士学位高一点），“优等生”或“受表扬”。这是在杰拉德线继续博士学位，但在那个时候，没有空缺在范特霍夫实验室在乌得勒支。然而，汉斯确实在他的年轻团队中有一个职位，在瓦赫宁根大学，当时被称为“农业大学”。尽管大学的名称中有一个形容词，但仍然有更多的基础研究空间，Gerard很容易被激励，研究聚合物与界面的相互作用及其对胶体稳定性的影响将构成博士研究的一个有前途的挑战。这一研究始于1966年，描述当时对胶体稳定性的认识是很有趣的。当时，DLVO部分或多或少是熟悉的，Stern部分作为解释离子特异性的有用补充。聚合物的作用被笼罩在神秘之中。众所周知，聚合物可以使溶胶稳定（保护），也可以使溶胶封闭（敏化或吸附封闭）。其中一个参数是“黄金数”，即保护Au溶胶不受NaCl凝固影响所需的亲水胶体量。然而，事实上，一个给定的聚合物可以要么封闭或保护一个给定的溶胶，取决于聚合物的浓度，仍然是一个谜。直觉告诉我们线索应该存在于聚合物在粒子表面的吸附。考虑到这一点，杰拉德开始着手工作，第一个问题是系统的选择。选择了银作为疏水胶体--荷兰学派的经典范例。我们在熟悉的领域。我们已经知道如何使溶胶和悬浮液稳定和静电稳定，界面电化学已得到控制，低分子量物质的吸附等温线已被详细研究[1]。这个决定是相当武断的;我们不知道哪种聚合物的性质会起作用，而PVA起到了双重作用，它可以稳定溶胶，也可以测量它在悬浮液上的吸附。后来我们有了比色法。PVA有不同的摩尔质量和不同的亲水度（取代度），所以有不同的变量可以使用。典型地，在那个时间，聚合物溶胶和分散体都不均匀，均匀分散的AgIsol在那个时间可以形成，但是它们不能以微量形成，并且其表面性质与“经典“溶胶不同;例如，零电荷点非常不同。在Gerard的实际操作中，AgI-PVA系统非常好地达到了目的。吸附等温线的第一个发现之一是，它显示出高亲和力的特征。（最初加入的PVA吸附量最大）在平台区，吸附量随M和PVA疏水性的增加而增加。现在人们会说，平台吸附随着溶剂水质量的降低而增加。所有这一切现在都很熟悉，但当时这些趋势还没有牢固确立，Gerardswork [2]肯定是一个趋势的制定者。另一个观察结果是，吸附平衡的缓慢建立和明显的不可逆性将成为进一步发展的关键因素。Gerard工作方法的一个典型特征是发现了现在称为“混合方法”的方法[3]。当时，在水净化中使用聚合物作为絮凝剂，

Gerard Fleer“Daar heb je een goeie aan” With this brief Dutch sentence TheoOverbeek recommended and characterized Gerard to Hans Lyklema,with whom he was starting his PhD study at Wageningen University.The sentence is difﬁcult to translate, but means something like “Thereyou have a top notch man” Overbeeks high expectations were fullyvindicated by the ensuing career of the young student and now, fortyyears later, it is obvious that Gerard lived up to the high expectations.So, there is plenty reason to honour him in a special issue of Advancesin Colloid and Interface Science.Overbeeks favourable assessment of his promising student waspartlybasedonGerardsexcellentgradesintheﬁeldsofchemistryandphysics at Utrecht University and partly on his personal judgment.Gerard passed his ﬁnal university examination (at that time called“doctoral examination,” a degree somewhat above that of a presentMSc), “cum laude” or “with commendation.” It was in Gerards line tocontinue for a PhD but at that time there were no vacancies at theVan't Hoff laboratory in Utrecht. However, Hans did have a positionavailable in his young group at Wageningen University, which at thattime was called “Agricultural University.” Notwithstanding theadjective in the name of the university, there was room for morebasic studies and Gerard was easily motivated that studies on theinteraction of polymers with interfaces and its effect on colloidstability would constitute a promising challenge for a PhD study. Thisresearch started in 1966.It is interesting to describe the state of knowledge in colloidstability at that time. At that time the DLVO part was more or lessfamiliar, with the Stern part as a useful addendum to account for ionspeciﬁcity. The effect of polymers was shrouded in mystery. It wasknown that polymers could stabilize sols (protection) or that theycould ﬂocculate them (sensitization or adsorption ﬂocculation).Systematic quantitative data were rare and ad hoc, depending onthe system. One of the parameters was the “Gold number,” that is theamount of hydrophilic colloid needed to protect a Au sol againstcoagulation by addition of NaCl. However, the fact that a givenpolymer could either ﬂocculate or protect a given sol, depending onthe polymer concentration, remained enigmatic. Intuition told thatthe clue shouldresidein the adsorptionof the polymeron the particlesurface. With this in mind Gerard set to work.The ﬁrst issue was the choice of the system. As the hydrophobiccolloid the classical paradigm of the Dutch school, silver iodide waschosen. Here we were on familiar territory. We knew how to prepareand electrostatically stabilize sols and suspensions, the interfacialelectrochemistry was under control and adsorption isotherms of low-Msubstanceshadbeenstudiedindetail[1].Asthepolymerpoly(vinylalcohol) (PVA) was chosen. This decision was rather arbitrary; wewere at a loss which polymer properties would play a role, and PVAserved the dual purpose that it could stabilize the sols and that itsadsorptiononthesuspensioncouldbemeasured.Forthelatterwehadacolorimetricmethod.ThePVAcameinvariousmolecularmassesandin different degrees of hydrophilicity (degrees of substitution), sothere were variables to play with. Typically for that time, neither thesolnorthepolymerwashomodisperse.HomodispererseAgIsolscouldbemadeatthattime,buttheycouldonlybemadeinminutequantitiesanditssurfacepropertiesdifferedfromthe“classical”sols;forexamplewasthepointofzerochargeverydifferent.IntheablehandsofGerardthe AgI-PVA system served its purpose very well.One of the ﬁrst ﬁndings in the adsorption isotherms was that allexhibited high-afﬁnity character (the initially added PVA adsorbsalmost quantitatively) and that in the plateau region the adsorptionincreases with M and with increasing hydrophobicity of the PVA.Nowadays one would say that the plateau adsorption increases withdecreasing quality of the solvent water. All of this is now familiar, butat that time these trends were not yet ﬁrmly established and Gerardswork [2] was certainly a trend-setter. Another observation, the slowestablishment of adsorption equilibrium and the apparent irrevers-ibility would become a key ingredient in the further developments.One typical event, characteristic for Gerards way of working wasthe discovery of, what is now called the “mixing method” [3]. At thattime the using of polymers as ﬂocculants in water puriﬁcation was

Advances in Colloid and Interface Science

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