Designing a polymer coating process

[chill_factor]

Hi everybody.

My goal is to design a process that, with no automated machinery (I'm using a mechanical pipette), would allow for extremely uniform coverage (that is, with minimal area of multilayers or empty spaces) of a hydrophilic surface with a thin film of polymer solution.

I would also like some pointers on where to get help on writing a mathematical model for this.

I am using a stock polymer suspension in water. The concentration of this suspension can be varied widely. Currently I'm taking a small microliter size portion of this stock suspension and dripping it onto the surface of a substrate cut into exactly 1 cm2 squares. Then I let it dry. This seems too crude. I'm thinking of adding additives such as detergents or other polymers, changing temperature, or changing humidity, but would like a mathematical model to help guide my experiment.

how do I define the conditions such that the sample is dry and only the polymer remains?

how do I calculate the distribution of the polymers on the surface? Is there an analytical model? It is NOT uniform because the polymers are concentrated along the drying front; as water evaporates, the polymers do not, and get concentrated, yet diffusion of the polymers in water is much slower than evaporation (by my observations), and they get 'stuck' on the edges.

I keep looking at the diffusion equation and I have no idea how to use it, but there's no other equation to use.

 

[chemisttree]

Can you spin coat?
Or use a polymerizable surfactant or a CVD process as is used in parylene coatings?

 

[chill_factor]

Can you spin coat?
Or use a polymerizable surfactant or a CVD process as is used in parylene coatings?

the spincoating article is helpful. we cannot use CVD; we can't handle reactive gases. all we can do is sputtering. MAYBE we can do substrate bias and sputter the substrate itself, that would actually open up a lot of new structural motifs. I think I've already found a related article.

thank you so much for the help.

 

[chemisttree]

A polymerizable thiol terminated surfactant would coat a gold sputtered surface in a monolayer from solution and should be robust enough to remain intact during rinsing. Fairly straightforward manipulation, IMO.

 

[alphy]

I would suggest starting by breaking down the process into smaller steps and identifying the key variables that can affect the uniformity of the coating. These variables could include the concentration of the polymer suspension, the speed and method of adding the suspension to the substrate, the drying conditions (temperature, humidity), and any additives that may be added.

To design a mathematical model, you could use principles of mass transfer and diffusion to determine the distribution of the polymers on the surface. The diffusion equation can be used to calculate the concentration gradient of the polymer solution as it dries on the surface. You can also consider the effects of surface tension, viscosity, and any other physical properties of the polymer solution.

In order to ensure that the sample is completely dry and only the polymer remains, you could monitor the drying process using techniques such as weighing the sample at different intervals or using a drying oven to control the temperature and humidity. This will help you determine the optimal conditions for drying the sample and achieving a uniform coating.

Additionally, you could consider using techniques such as spin coating or dip coating to apply the polymer solution onto the substrate, which may result in a more uniform coating compared to the manual pipetting method.

It may also be helpful to consult with experts in the field of polymer coatings or reach out to academic institutions or research organizations for guidance on developing a mathematical model for your specific process. Collaborating with other scientists and researchers can provide valuable insights and help refine your experimental design.

Overall, designing a polymer coating process requires careful consideration of various factors and a systematic approach to optimize the conditions for achieving a uniform coating on the hydrophilic surface. Good luck with your research!