PDMS spreading morphological patterns on substrates of different hydrophilicity in air vacuum and water

In paper has been to investigate the morphological patterns and kinetics of PDMS spreading on silicon wafer using combination of techniques like ellipsometry, atomic force microscope (AFM), scanning electron microscope (SEM) and optical microscopy. A macroscopic silicone oil drops as well as PDMS water based emulsions were studied after deposition on a flat surface of silicon wafer in air, water and vacuum. our own measurements using an imaging ellipsometer, which also clearly shows the presence of a precursor film. The diffusion constant of this film, measured with a 60 000 cS PDMS sample spreading on a hydrophilic silicon wafer, is Df = 1.4  10-11 m2/s. Regardless of their size, density and method of deposition, droplets on both types of wafer (hydrophilic and hydrophobic) flatten out over a period of many hours, up to 3 days. During this process neighbouring droplets may coalesce, but there is strong evidence that some of the PDMS from the droplets migrates into a thin, continuous film that covers the surface in between droplets. The thin film appears to be ubiquitous if there has been any deposition of PDMS. However, this statement needs further verification. One question is whether the film forms immediately after forced drying, or whether in some or all cases it only forms by spreading from isolated droplets as they slowly flatten out.

Polydimethylsiloxane (PDMS) modulates CD38 expression, absorbs retinoic acid and may perturb retinoid signalling

Polydimethylsiloxane (PDMS) is the most commonly used material in the manufacture of customized cell culture devices. While there is concern that uncured PDMS oligomers may leach into culture medium and/or hydrophobic molecules may be absorbed into PDMS structures, there is no consensus on how or if PDMS influences cell behaviour. We observed that human umbilical cord blood (CB)-derived CD34+ cells expanded in standard culture medium on PDMS exhibit reduced CD38 surface expression, relative to cells cultured on tissue culture polystyrene (TCP). All-trans retinoic acid (ATRA) induces CD38 expression, and we reasoned that this hydrophobic molecule might be absorbed by PDMS. Through a series of experiments we demonstrated that ATRA-mediated CD38 expression was attenuated when cultures were maintained on PDMS. Medium pre-incubated on PDMS for extended durations resulted in a time-dependant reduction of ATRA in the medium and increasingly attenuated CD38 expression. This indicated a time-dependent absorption of ATRA into the PDMS. To better understand how PDMS might generally influence cell behaviour, Ingenuity Pathway Analysis (IPA) was used to identify potential upstream regulators. This analysis was performed for differentially expressed genes in primary cells including CD34+ haematopoietic progenitor cells, mesenchymal stromal cells (MSC), and keratinocytes, and cell lines including prostate cancer epithelial cells (LNCaP), breast cancer epithelial cells (MCF-7), and myeloid leukaemia cells (KG1a). IPA predicted that the most likely common upstream regulator of perturbed pathways was ATRA. We demonstrate here that ATRA is absorbed by PDMS in a time-dependent manner and results in the concomitant reduced expression of CD38 on the cell surface of CB-derived CD34+ cells.

Surface modification of PDMS using atmospheric glow discharge polymerization of tetrafluoroethane for immobilization of biomolecules

In this study an atmospheric glow discharge with a fluorocarbon gas as precursor was used to modify the surface of polydimethyl siloxane (PDMS -(CH3)(2)SiO](n)-). The variation in protein immobilizing capability of PDMS was studied for different times of exposure. It was observed that the concentration of proteins adsorbed on the surface varied in an irregular manner with treatment time. The fluorination results in the formation of a thin film of fluorocarbon on the PDMS surface. The AFM and XPS data suggest that the film cracks due to stress and regains its uniformity thereafter. This Stranski-Krastanov growth model of the film was due to the high growth rate offered by atmospheric glow discharge. (C) 2011 Elsevier B. V. All rights reserved.

The Nonlinear Phenomena Of Thin Polydimethylsiloxane (Pdms) Films In Electrowetting

Electrowetting (EW) is an effective way to manipulate small volume liquid in micro- and nano-devices, for it can improve its wettability. Since the late 1990s, electrowetting-on-dielectric (EWOD) has been used widely in bio-MEMS, lab-on-a-chip, etc. Polydimethlsiloxane (PDMS) is extensively utilized as base materials in the fabrication of biomedical micro- and nano-devices. The properties of thin PDMS films used as dielectric layer in EW are studied in this paper. The experimental results show that the thin PDMS films exhibit good properties in EWOD. As to PDMS films with different thicknesses, a threshold voltage and a hysteresis were observed in the EIWOD experiments.

Role Of Vertical Component Of Surface Tension Of The Droplet On The Elastic Deformation Of Pdms Membrane

Poly(dimethylsiloxane) (PDMS) has been widely used in lab-on-a-chip and micro- total analysis systems (mu-TAS), thus wetting and electrowetting behaviors of PDMS are of great importance in these devices. PDMS is a kind of soft polymer material, so the elastic deformation of PDMS membrane by a droplet cannot be neglected due to the vertical component of the interfacial tension between the liquid and vapor, and this vertical component of liquid-vapor surface tension is also balanced by the stress distribution within the PDMS membrane. Such elastic deformation and stress distribution not only affect the exact measurement of contact angle, but also have influence on the micro-fluidic behavior of the devices. Using ANSYS code, we simulated numerically the elastic deformation and stress distribution of PDMS membrane on a rigid substrate due to the liquid-vapor surface tension. It is found that the vertical elastic deformation of the PDMS membrane is on the order of several tens of nanometers due to the application of a droplet with a diameter of 2.31 mm, which is no longer negligible for lab-on-a-chip and mu-TAS. The vertical elastic deformation increases with the thickness of the PDMS membrane, and there exists a saturated membrane thickness, regarded as a semi-infinite membrane thickness, and the vertical elastic deformation reaches a limiting value when the membrane thickness is equal to or thicker than such saturated thickness. (C) Koninklijke Brill NV, Leiden, 2008.

Influence Of Different Amount Of Au On The Wetting Behavior Of Pdms Membrane

Polydimethylsiloxane (PDMS) has been widely used as a base material for bio-MEMS/NEMS devices. It is difficult for PDMS to transfer and spread aqueous solution as a kind of highly hydrophobic material. Therefore, surface modification is necessary for PDMS to make it hydrophilic. In this paper, a method of hydrophilization of PDMS surface is proposed. Gold is sputtered to the PDMS substrate by sputter coater in different average thicknesses. Relationship between the average thickness of gold on the PDMS substrate and the contact angle of the surface was studied. It was found that even gold of average thickness less than 1 nm can result in about 25 degrees change of contact angle. AFM is also used to get topographic information of PDMS surface coated with gold. Three cases are classified with different amount of Au: (1) Heterogeneous zone; (2) Transition zone; (3) Film zone. For heterogeneous zone, a simple model about heterogeneous phase wetting is put forward to interpret this phenomenon.

一种PDMS薄膜型微阀的制备与性能分析

通过厚胶光刻工艺在硅片上制备SU 8胶模板,利用该模板制备了高分子聚合物PDMS(Polydimethylsiloxane,聚二甲基硅氧烷)微流道和薄膜结构。通过对不同结构的两层PDMS的不可逆粘接得到一种简单的阀结构,在外加气源压力作用下薄膜产生变形实现对微流道的控制。实验测量了微阀的控制气源压力与被控制液体流量之间的关系,说明膜阀的开闭性能良好。根据弹性薄膜的变形理论,对影响微阀性能的参数进行了分析,并提出了几种可行的用于薄膜微阀控制的方法。

Deformation Of Pdms Membrane And Microcantilever By A Water Droplet: Comparison Between Mooney-Rivlin And Linear Elastic Constitutive Models

In this paper, we studied the role of vertical component Of Surface tension of a water droplet on the deformation of membranes and microcantilevers (MCLs) widely used in lab-on-a-chip and micro-and nano-electromechanical system (MEMS/NEMS). Firstly, a membrane made of a rubber-like material, poly(dimethylsiloxane) (PDMS), was considered. The deformation was investigated using the Mooney-Rivlin (MR) model and the linear elastic constitutive relation, respectively. By comparison between the numerical solutions with two different models, we found that the simple linear elastic model is accurate enough to describe such kind of problem, which would be quite convenient for engineering applications. Furthermore, based on small-deflection beam theory, the effect of a liquid droplet on the deflection of a MCL was also studied. The free-end deflection of the MCL was investigated by considering different cases like a cylindrical droplet, a spherical droplet centered on the MCL and a spherical droplet arbitrarily positioned on the MCL. Numerical simulations demonstrated that the deflection might not be neglected, and showed good agreement with our theoretical analyses. (C) 2008 Elsevier Inc. All rights reserved.

聚二甲基硅氧烷（PDMS）表面液滴动力学的实验研究

液滴是自然界中普遍存在的一种物质形态。非连续微流体（液滴）是近年来微流体技术重要发展方向之一。对液滴的产生、启动、移动、合并、分离和碰撞过程的研究对于航天、微纳系统、电子显示、计算机冷却、喷墨、生物医学等学科领域有着重要的应用价值。液滴属于软物质，其力学性质介于流体和固体之间，其类固体（solid-like）行为来自于曲率产生的Laplace压力和表面张力的约束。对液滴动力学行为的研究有着重要的学术价值。 本文的主要工作是针对生物微电子机械系统（Bio-MEMS）以及柔性微纳电子加工中常用的材料聚二甲基硅氧烷（Polydimethylsiloxane，PDMS）为基底的液滴动力学实验研究。 液滴是一个理想的微反应器，许多实验可以集成在一个液滴或多个液滴内完成。液滴本身的动力学特性对于实验的完成效率和质量有着重要的影响。液滴的微操控技术包括多相流法、电润湿法、热毛细管法、介电泳法等。液滴的动力学特性受到基底的影响非常大，包括基频、振动模态、运动过程等均随基底的润湿性、弹性模量的变化而有所变化。 在Bio-MEMS以及柔性微纳电子加工当中，PDMS扮演着越来越重要的角色，尤其是PDMS的润湿性和电润湿特性。目前的PDMS在Bio-MEMS当中主要是用于制备各种微流道。常见的问题主要是一方面PDMS是疏水材料，影响流体的输运。另一方面是液体在这种低Reynolds数情况下不易混合，反应效率低。本文提出了在PDMS表面溅射纳米厚度的金来减小PDMS表观接触角的方法。这种方式在特定喷金量的情况下可以在PDMS表面产生多层次的压应力波纹。这种压应力波纹对于柔性微纳电子加工，以及微流道中加速流体混合有着非常重要的作用。 电润湿是另一种可以使PDMS亲水化的方法。实验证明，PDMS具有较好的电润湿性质。此外电润湿也是目前操纵液滴的主要方式。目前一个常见的问题是电击穿现象阻碍了驱动电压的低压化，且低Reynolds数情况下液滴的混合效率偏低。此外电极还会由于少量电解的发生导致腐蚀及对液体样品的污染。本文提出了接触式的电润湿，在电极逐渐触碰液滴的过程中，液滴发生百Hz的失稳振动，稳定后接触角减小。这种电润湿模式可以有效的提高临界击穿电压，避免液滴被腐蚀后的电极污染，同时可以加快液滴的混合效率。其失稳特征时间在10 ms量级，这恰是所用液滴特征尺度在1 mm左右的电润湿器件的最快响应时间。并采用液滴振动的理论估算了液滴的失稳时间，同时还考虑了基底润湿性对液滴振动过程的影响。 液滴的启动是电润湿操控液滴过程中的重要环节。通常的液滴启动都是在非连续基底上依靠逻辑电路产生的电势变化来驱动液滴。无论是逻辑电路的设计还是驱动装置的加工都非常复杂。本文首次实现了在超疏水生物样品荷叶上的液滴启动，启动速度为数十毫米/秒，启动时间为10 ms量级。并利用PDMS成功的仿制了荷叶结构实现了超疏水的PDMS表面，荷叶同仿荷叶的PDMS超疏水表面具有相近的润湿性。 在数字微流体操控液滴的过程中，液滴的合并涉及液滴的碰撞，而且MEMS系统当中利用液滴撞击进行冷却的实验已经有所开展。同时理解液滴碰撞还对许多领域包括生物、化学、喷墨、大气物理等有着非常重要的作用。本文实验研究了Weber数和毛细数对液滴碰撞过程的影响，通过改变Weber数和毛细数得到了四种不同的响应模式。