Mobility of functionalized quantum dots and a model polystyrene nanoparticle in saturated quartz sand and loamy sand

Quantum dots (QDs) are one example of engineered nanoparticles (ENPs) with demonstrated toxic effects. Yet, little is known about the behavior of QDs in the natural environment. This study assessed the transport of two commercial carboxylated QDs (CdTe and CdSe) and carboxylated polystyrene latex (nPL) as a model nanoparticle using saturated laboratory-scale columns. The influence of solution ionic strength (IS) and cation type (K(+) or Ca(2+)) on the transport potential of these ENPs was examined in two granular matrices - quartz sand and loamy sand. The retention of all three particles was generally low in the quartz sand columns within the range of studied IS (0.1-100 mM) for the monovalent salt (KCl). In contrast, the retention of the three ENPs in the quartz sand was significant in the presence of 10 mM Ca(2+). Moreover, ENP attachment efficiencies (α) were enhanced by at least 1 order of magnitude in columns packed with loamy sand (for IS between 0.1-10 mM KCl). Although all three ENPs used here are carboxylated, they differ in the type of surface coating (e.g., choice of polymers or polyelectrolytes). Regardless of the surface coatings, the three ENPs exhibit comparable mobility in the quartz sand. However, the ENPs demonstrate variable transport potential in loamy sand suggesting that differences in the binding affinities of surface-modified ENPs for specific soil constituents can play a key role in the fate of ENPs in soils.     

Role of Pseudomonas aeruginosa biofilm in the initial adhesion, growth and detachment of Escherichia coli in porous media

This study systematically investigated the impact of Pseudomonas aeruginosa biofilm on the initial adhesion, growth, and detachment of indicator bacteria Escherichia coli JM109 in porous media. Two P. aeruginosa strains, the mucoid PD0300 and wide type PA01 with different extracellular polymeric substance (EPS) composition and secretion capability, were used to grow biofilm in packed beds. Results from the column breakthrough curves and retained JM109 profiles show that the amount and composition of P. aeruginosa biofilm EPS have a profound impact on the deposition and retention of E. coli in porous media. PAO1 biofilm coating improved E. coli retention in the column, whereas PDO300 biofilm coating had only a small impact on E. coli removal. Biofilm surface hydrophobicity and polymeric interactions between the biofilm and E. coli cell surfaces were found to play important roles in controlling the distribution of E. coli along the columns. After initial attachment, E. coli bacteria were able to survive and grow at similar growth rates in columns coated with either PAO1 or PDO300 biofilms with a relatively low nutrient supply. Biofilm detachment was the major mechanism that introduced E. coli bacteria to the bulk fluid long after the contamination event when E. coli cells became an integral part of the biofilm. Findings of this study suggest that biofilm plays a significant role in controlling the initial attachment, growth, and survival of bacteria in porous media, and that the interaction between bacteria and biofilm surfaces should be considered when predicting bacterial and pathogen migration in the environment.     

Distribution of colloid particles onto interfaces in partially saturated sand

Colloids have long been known to facilitate the transport of contaminants in soils, but few direct observations have been made of transport and retention in unsaturated porous media. Studies have typically been limited to evaluation of column breakthrough curves, resulting in differing and sometimes conflicting proposed retention mechanisms. We carried out pore scale visualization studies of colloid transport in unsaturated quartz sand to directly observe and characterize colloid retention phenomena. Synthetic hydrophilic (0.8, 2.6, and 4.8 microm carboxylated polystyrene latex) and relatively hydrophobic (5.2 microm polystyrene latex) colloidal microspheres were added to steady-state water flow (0.15 mm min(-1)) applied to an inclined infiltration chamber. Bright field microscopy was used to determine the positions and movement of water and colloids. Confocal laser scanning microscopy was used to determine water film geometry in an unsaturated horizontal chamber. We determined mechanisms of hydrophilic colloid retention at what is generally termed the air/water/solid (AWS) interface. Based on our observations, the AWS interface is here more accuratelytermed the air/water meniscus/solid (AWmS) interface, denoting the region where between-grain water meniscii diminish to thin water films on the grain surfaces. Colloids were retained at the AWmS interface where the film thickness approximately equaled colloid diameters. The greater retention for hydrophilic colloids at this interface (compared to elsewhere in the solid/water interface) can be explained by the additional surface tension capillary potentials exerted on colloids at the AWmS interface. While some 0.8-microm colloids were observed in thin water films, film straining played no significant role in the retention of larger colloids. Mechanisms for slightly hydrophobic colloids differed slightly. In addition to primary retention at the AWmS interface, hydrophobic colloids attached to others already present atthat interface resulting in apparent retention at the air/water (AW) interface. Attachment of hydrophobic colloids was also observed at water-solid interfaces, as hydrophobicity impelled the colloids to avoid water. Factors contributing to retention of slightly hydrophobic colloids were sand grain roughness and possibly a tendency for these colloids to flow near surfaces and interfaces, consonant with the enhanced retention of hydrophobic colloids (relative to hydrophilic colloids) observed in the literature.     

Adhesion and retention of a bacterial phytopathogen Erwinia chrysanthemi in biofilm-coated porous media

The goal of this study is to investigate the impact of biofilm physical and biological properties on bacterial transport and deposition in porous media. Experiments were performed in packed columns to examine the removal of Erwinia chrysanthemi (Ech3937), a phytopathogen, from the bulk fluid due to its attachmentto glass beads coated with Pseudomonas aeruginosa biofilms. Two isogenic P. aeruginosa strains, PAO1 and PD0300, with different EPS secretion capabilities and EPS compositions, were used to culture biofilms. The Ech3937 transport and distribution in packed columns were studied in both upflow and downflow cell injection modes over a range of solution ionic strengths. The results show that the presence of biofilm strongly interferes with the deposition behavior of Ech3937 in porous media. The spatial variation of deposited Ech3937 cells contradicts the log-linear pattern predicted by the classic filtration theory, indicating that the biofilm physical structure and polymeric interactions between the biofilm EPS and Ech3937 cell surface are the main mechanisms that control bacterial deposition. When the biofilm accumulation is relatively small, bacterial adhesion onto biofilm-coated porous media is mainly inhibited by steric forces. By contrast, cell deposition is enhanced by the reduced porous media porosity when biofilm is more abundant.     

Commercial titanium dioxide nanoparticles in both natural and synthetic water: comprehensive multidimensional testing and prediction of aggregation behavior

Engineered nanoparticles (ENPs) from industrial applications and consumer products are already being released into the environment. Their distribution within the environment is, among other factors, determined by the dispersion state and aggregation behavior of the nanoparticles and, in turn, directly affects the exposure of aquatic organisms to EPNs. The aggregation behavior (or colloidal stability) of these particles is controlled by the water chemistry and, to a large extent, by the surface chemistry of the particles. This paper presents results from extensive colloidal stability tests on commercially relevant titanium dioxide nanoparticles (Evonik P25) in well-controlled synthetic waters covering a wide range of pH values and water chemistries, and also in standard synthetic (EPA) waters and natural waters. The results demonstrate in detail the dependency of TiO(2) aggregation on the ionic strength of the solution, the presence of relevant monovalent and divalent ions, the presence and copresence of natural organic matter (NOM), and of course the pH of the solution. Specific interactions of both NOM and divalent ions with the TiO(2) surfaces modify the chemistry of these surfaces resulting in unexpected behavior. Results from matrix testing in well-controlled batch systems allow predictions to be made on the behavior in the broader natural environment. Our study provides the basis for a testing scheme and data treatment technique to extrapolate and eventually predict nanoparticle behavior in a wide variety of natural waters.     

Retention and transport of amphiphilic colloids under unsaturated flow conditions: effect of particle size and surface property

The purpose of this study was to examine the mechanisms responsible for deposition and transport of amphiphilic colloids with a wide range of particle sizes (20-420 nm) through porous media. A series of saturated and unsaturated column experiments were conducted using amphiphilic latex microspheres and a hydrophilic silica colloid. We found that the amphiphilic latex particles were retained to a greater extentthan the hydrophilic silica colloid in unsaturated media. This was attributed to colloidal attachment atthe air-water interface due mainly to hydrophobic interactions. We also found that dependence of colloid retention on particle size was nonlinear. There existed a fraction of colloids with greater mobility than other fractions, which we referred to as the most mobile colloids. As particle size increased from 20 to 420 nm, colloid deposition rate first decreased to reach a minimum value at --100 nm then increased, indicating that different retention mechanisms were involved. We showed that conducting saturated transport experiments and analysis using filtration theory may be an effective approach for determining the most mobile colloid size(s) in porous media, perhaps even for unsaturated flow conditions. This study highlights the importance of including size effect and surface properties when predicting concentrations and fluxes of amphiphilic colloids or colloid-bound amphiphilic and hydrophobic contaminants in the subsurface environment.     

Influence of extracellular polymeric substances on Pseudomonas aeruginosa transport and deposition profiles in porous media

The impact of cell surface extracellular polymeric substances (EPS) on bacterial transport and retention profiles was investigated in saturated columns packed with glass beads. Three genetically well-defined isogenic Pseudomonas aeruginosa strains with different EPS secretion capability and EPS composition were used to systematically examine their deposition behavior over a range of solution chemistry. The presence of EPS on nonmucoid strain PA01 and mucoid strain PD0300 significantly increased bacterial adhesion over the EPS deficient PA01 psl pel mutant strain despite their similar surface charge as indicated by the zeta potential measurements. Retained bacterial profiles show the deposition rate coefficients with various shapes and degrees of deviation from those expected from the classic filtration theory. Non-monotonic deviations from the log-linear deposition pattern with the majority of the bacteria retained downgradient of the column inlet were observed when bacterial cells were encapsuled by EPS under both high and low ionic strength conditions. In contrast, the EPS-deficient strain exhibited monotonic deviation from theory only under low ionic strength conditions. The results demonstrate that the non-monotonic deviation from filtration theory observed in this study was driven by steric interactions between extracellular polymers and glass beads. Analysis of the retained polysaccharides (carbohydrates and uronic acids) and protein profiles suggests that bacterial re-entrainment and re-entrapment may have contributed to the downgradient movement of the maximum retained bacteria. The detachment of bacteria may leave behind various constituents of EPS as their "footprints," which can be a valuable tool for tracking the trajectory of bacterial transport.     

填料特性对层间加填成纸性能的影响

层间加填是将矿物填料直接添加在纸页层间,有利于提高填料在纸页中的留着率、降低白水浊度和优化抄纸湿部化学环境等。本实验选用滑石粉和碳酸钙为矿物填料,羧基丁苯胶乳为层间黏合剂,对瓦楞原纸成形过程中填料的形状、粒径对成纸物理强度的影响进行了研究。结果表明:在其他条件不变的情况下,以碳酸钙为填料的成纸物理强度性能优于滑石粉。当碳酸钙用量为25%(对绝干浆),羧基丁苯胶乳用量为2%时,以全废纸抄造瓦楞原纸的相关物理强度指标可达到国家标准(GB 13023-1991)要求。     

Kinetics of coupled primary- and secondary-minimum deposition of colloids under unfavorable chemical conditions

This study examines the deposition/release mechanisms involved in colloid retention under unfavorable conditions through theoretical analysis and laboratory column experiments. A Maxwell approach was utilized to estimate the coupled effects of primary- and secondary-minimum deposition. Theoretical analysis indicates that the secondary energy minimum plays a dominant role in colloid deposition even for nanosized particles (e.g., 20 nm) and primary-minimum deposition rarely happens for large colloids (e.g., 1000 nm) when diffusion is the dominant process. Polystyrene latex particles (30 and 1156 nm) and clean sand were used to conduct three-step column experiments at different solution ionic strengths, a constant pH of 10, and a flow rate of 0.0012 cm/s. Experimental results confirm that small colloids can also be deposited in secondary minima. Additional column experiments involving flow interruption further indicates that the colloids deposited in the secondary energy well can be spontaneously released to bulk solution when the secondary energy minimum is comparable to the average Brownian kinetic energy. Experimental collision efficiencies are in good agreement with Maxwell model predictions but different from the theoretical values calculated by the interfacial force boundary layer approximation. We propose a priori analytical approach to estimate collision efficiencies accounting for both primary- and secondary-minimum deposition and suggest that the reversibility of colloid (e.g., viruses and bacteria) deposition must be considered in transport models for accurate predictions of their travel time in the subsurface environments.     

单一胶粘剂对涂料流变性的影响

对常用的氧化淀粉、羧基丁苯胶乳和聚乙烯醇在不同的添加量情况下配成的涂料进行了系统的研究,结果表明涂料都呈剪切稀化特性,通过对实验结果进行多次分析,认为用修改的幂律方程表达很理想。     

TAPPI JOURNAL 2018年第10期目次

本实验建立在之前对含淀粉乳胶涂料的流变特性和动态保水性的研究成果基础之上。前期研究表明,淀粉胶乳的流变性和动态保水性不同于传统熟化涂布淀粉。本实验采用血清置换法研究了水膨胀淀粉纳米粒子的基本性能及其胶体行为。结果表明,淀粉胶乳是由微粒和少量可溶性聚合物组成的复杂体系。提高交联度会减少可溶性组分,并降低分散黏度。实验室圆柱形涂布机形成的涂层显示,丁苯胶乳具有可塑性,在压光过程中起到润滑剂的作用,有助于提高纸张光泽度。将生物胶乳与羟乙基淀粉（接枝聚合物）交联可以提高涂料的保水性,但是低交联Bio-A的使用则会降低涂布纸的光泽度。     

Preparation of Ultrafine Starch Particle and its Application in Paper Coating

Despite its biodegradability, adequate cohesive strength and comparatively low cost, the use of cooked starch as a paper coating binder is limited due to its high viscosity and serious negative impact on the gloss. Starch-based bio-latex with size in the nanometer or sub-micrometer range has been developed recently to overcome these shortcomings. In this study, ultrafine starch particle (UFSP) was prepared by mechanical milling using a DYNO mill in combination with light chemical pretreatment. Model coating colors containing different dosages of UFSP were applied to base paper and the properties of the coated papers were evaluated. The results showed that the UFSP was disc-shaped with a median particle diameter of 167 nm. Water retention capacity of the coating colors was improved considerably with the addition of UFSP, i.e., the water retention value decreased by nearly 40% when styrene-butadiene latex was replaced by UFSP at a dosage of 3 pph (per hundred parts of pigment). The high shear rate viscosities of the coating colors containing no more than 2 pph of USFP were similar to that of the control coating color at shear strain rate higher than 2000 s1. The properties and performances of the coated papers were comparable to the control coated paper with single synthesized latex binder. The gloss and the print gloss of paper samples with or without USFP were 59.7% and 58.2%, 79.0% and 78.8%, respectively. Surface strength of paper samples with or without USFP were 0.96 and 0.90 m/s, respectively, while the ink absorptivity values were 34% and 33%. This study demonstrates a promising approach to obtain sub-micrometer sized starch for paper coating.     

水牛乳中高产胞外多糖乳酸菌的筛选与鉴定

从生水牛乳中筛选出两株高产胞外多糖（EPS）的乳酸菌株LB2、LB7,经MRS肉汤培养基发酵后,菌液中的胞外多糖（EPS）产量分别达135 mg/L、148 mg/L,通过形态学、生理生化特征、API细菌鉴定系统、16S rRNA序列分析,鉴定出菌株LB2为植物乳杆菌（Lactobacillus plantarum）,LB7为类肠膜魏斯氏菌（Weissella paramesenteroides）。将其应用到水牛乳酸奶的发酵中,结果表明,植物乳杆菌LB2和类肠膜魏斯氏菌LB7均可用来发酵水牛乳酸奶,且能有效增加酸奶的黏度和胞外多糖产量,其黏度和EPS产量分别为4 050 mPa·s和149 mg/L。     

淀粉-脂肪酸复合物包覆改性硅藻土的制备及表征

采用淀粉-脂肪酸复合物对硅藻土进行包覆改性,研究了淀粉-脂肪酸复合物对硅藻土的包覆效果、改性硅藻土的留着率及抗剪切性能;采用扫描电子显微镜、Zeta电位仪、粒度分析仪对改性硅藻土进行表征。结果表明,淀粉-脂肪酸复合物可有效包覆硅藻土,淀粉沉积率达98%以上;与未改性硅藻土相比,改性硅藻土的Zeta电位高,抗剪切性能好;当改性硅藻土添加量为10%时,其留着率超过73%。     

涂层固化过程中胶乳粒子迁移的机理（Ⅱ）

研究了涂布纸涂层固化过程中胶乳粒子向涂层表面发生迁移的现象,对此提出了一种新的基于Einstein经典粒子扩散理论和表面效应的机理来进行解释,澄清了涂料及相关领域对粒子迁移机理的争议。以微米级高岭土、亚微米级羧基丁苯胶乳为主要原料制备涂料进行涂布,用 X射线光电子能谱仪（XPS）检测涂层表面的元素组成和含量,建立了原子数比值与胶乳用量之间的回归方程;通过该方程将不同条件下固化的涂层表面XPS检测结果转化为表面胶乳含量,定量分析了不同因素对胶乳粒子迁移程度的影响。结果表明,干燥温度升高、高温干燥时间延长、涂料初始固含量降低会促进胶乳向涂层表面迁移,而胶乳粒径增大、涂料黏度增加、基质吸收性增强会抑制其迁移,验证了新机理的合理性。     

Anionic homopolymers efficiently target zerovalent iron particles to hydrophobic contaminants in sand columns

The transport of microscale carbonyl iron powder suspensions modified with anionic homopolymers was studied in water-saturated sand columns containing well-dispersed hydrophobic sand grains. Sand grains functionalized with hexadecyltrimethoxysilane were coated with a eutectic mixture of dichlorobenzenes that was solid at -10 °C and was mixed by grinding with unmodified sand grains. The dichlorobenzene coating liquefied at the temperature of the transport experiments, and the coated grains were thus mimetic of uniform droplets of dense nonaqueous phase liquid (DNAPL) contaminants. By comparing iron particle transport in uncontaminated columns with those that contained a small fraction of DNAPL-coated sand grains, sticking coefficients for both types of grains could be estimated. The anionic polyelectrolytes tested (polyacrylate, carboxymethylcellulose, alginate, and metasilicate) all gave low particle sticking coefficients (0.004-0.05) to unmodified sand, as expected from earlier studies. However, iron particles modified with the two moderately hydrophobic polymers (carboxymethylcellulose and polyacrylate) had 30-fold higher sticking coefficients (0.40 and 0.13, respectively) to the model DNAPL surface than they did to the sand surface. In contrast, no significant difference between the two kinds of collector grains was found with the more polar polymers (metasilicate and alginate). The trend in sticking coefficients was correlated with the surface energy of the polymer-modified iron surface as measured by the static contact angle method. From these data one can conclude that the hydrophobicity of the polymer dispersant is a key factor in targeting zerovalent iron to DNAPL source zones in soil and groundwater.     

纤维基超疏水功能表面制备方法的研究进展

超疏水表面因其优越的拒水性和自清洁能力,成为新材料研究的热点。超疏水功能表面的应用领域与其表面基质息息相关,以纤维为基材制备的超疏水表面因其原料易得,应用范围广,并且有望实现工业化生产而得到重视。纤维基超疏水表面的制备方法主要有层层组装法、溶胶-凝胶法、水热法、纳米粒子负载法以及气象沉积法等,通过这些方法可以制备大面积、性能稳定的纤维基超疏水材料。本文对纤维基超疏水功能表面材料的制备方法进行了综述,并对超疏水表面的功能复合及研究发展趋势进行了展望。     

纳米TiO2胶体多元复配体系对DIP的助留助滤研究

利用动态滤水实验,通过检测留着率和滤水时间来考察纳米TiO2胶体多元复配体系对脱墨浆(DIP)抄造新闻纸过程的助留助滤作用.结果表明,二元体系中,AmS(两性淀粉)-TiO2二元复配体系助留助滤效果最好,当纳米TiO2胶体用量0.20％和AmS用量0.5％时,其滤水时间是13s,其总留着率达到93.4％;在三元体系中,当CS(阳离子淀粉)用量0.4％、APAM(阴离子聚丙烯酰胺)用量0.01％和纳米TiO2胶体用量0.2％时的体系的滤水时间最小,为17s;当CS用量0.4％、CPAM(阳离子聚丙烯酰胺)用量0.01％和纳米TiO2胶体用量0.2％时总留着率最大,为97.5％.研究发现,纳米TiO2胶体多元体系具有好的助留助滤效果,淀粉系列因为具有三维结构,为纤维、DCS(溶解和胶体物质)的絮聚提供了更多的结合机会,而PAM(聚丙烯酰胺)系列主要通过桥联、电荷吸附以及补丁絮聚机理实现好的助留助滤效果.     

COMPRESSION STRENGTH AND FRACTURE PROPERTIES OF MODEL PARTICULATE FOOD COMPOSITES IN RELATION TO THEIR MICROSTRUCTURE AND PARTICLE-MATRIX INTERACTION

Foods containing particles in a matrix were modelled by setting glass spheres, varying in size and surface chemistry, and oil droplets in heat-denatured whey protein gels. Composites containing particles with hydrophilic surfaces were much stronger in compression, the strength being dependent on particle surface area, than those with hydrophobia surfaces. The relationship between strength and particle size was compared with existing rheological and composite theories. SEM examination of fracture surfaces, resulting from compression, showed that particles with an hydrophilic surface were an integral part of the composite, failure occurring within the protein matrix. Gels made from particles with an hydrophobic surface fractured adjacent to the particle surface, indicating little or no interaction between particle and matrix.     

Humic acid facilitates the transport of ARS-labeled hydroxyapatite nanoparticles in iron oxyhydroxide-coated sand

Hydroxyapatite nanoparticles (nHAP) have been widely used to remediate soil and wastewater contaminated with metals and radionuclides. However, our understanding of nHAP transport and fate is limited in natural environments that exhibit significant variability in solid and solution chemistry. The transport and retention kinetics of Alizarin red S (ARS)-labeled nHAP were investigated in water-saturated packed columns that encompassed a range of humic acid concentrations (HA, 0-10 mg L(-1)), fractional surface coverage of iron oxyhydroxide coatings on sand grains (λ, 0-0.75), and pH (6.0-10.5). HA was found to have a marked effect on the electrokinetic properties of ARS-nHAP, and on the transport and retention of ARS-nHAP in granular media. The transport of ARS-nHAP was found to increase with increasing HA concentration because of enhanced colloidal stability and the reduced aggregate size. When HA = 10 mg L(-1), greater ARS-nHAP attachment occurred with increasing λ because of increased electrostatic attraction between negatively charged nanoparticles and positively charged iron oxyhydroxides, although alkaline conditions (pH 8.0 and 10.5) reversed the surface charge of the iron oxyhydroxides and therefore decreased deposition. The retention profiles of ARS-nHAP exhibited a hyperexponential shape for all test conditions, suggesting some unfavorable attachment conditions. Retarded breakthrough curves occurred in sands with iron oxyhydroxide coatings because of time-dependent occupation of favorable deposition sites. Consideration of the above effects is necessary to improve remediation efficiency of nHAP for metals and actinides in soils and subsurface environments.