Surfactants & Solvents: Potential for MCP-Designed Nanostructured Fluids for the Removal of Polymer Films

Now that it’s available in the Western Association for Art Conservation (WAAC) archive, I thought I’d post an updated version of a paper from 2020 on nanostructured fluids. You can download the updated pdf here.

Aside from the ludicrous title, it’s not bad. Especially if you’re interested in microemulsions, art conservation, and how conservators remove deteriorated coatings from artifacts without dissolving the coating (spoiler: by dewetting them). I’ve included a video below demonstrating the variable cloud point of a nonionic, PEG-based, surfactant solution upon addition of a hydrogen bond accepting (HBA) solvent, in this case propylene carbonate. If you’d like to learn more about cloud point temperatures and why you may (or may not) want to change them, take a look at the paper above.

Finally, any discussion of nanostructured fluids in art conservation would be remiss without mentioning Dr. Piero Baglioni and his phenomenal group at the University of Florence. They continue to spearhead the development and use of nanostructured fluids in art conservation, and have produced a staggering number of publications on the topic. Many can be found at Piero and Michele Baglioni’s (no relation) google scholar pages. Well worth the time for any conservator or interested chemist.

Conservation Consultations & Lectures

Teaching and lecturing online over the past year and a half has proven to be a great way to reach conservation students, emerging professionals, and colleagues. Earlier this year I also began doing online conservation consultations.

Those have ranged from quick chats with students and private conservators, to long-term research consultations and treatment walkthroughs with preservation departments at the Getty Museum, Library of Congress, and National Park Service. It has been a lot of fun and very rewarding.

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Photo Courtesy of W. Patrick Edwards: (BT) Louis XV Kingwood Clock, Gilt Bronze, c. 1730-1760.

Recently I was working via Zoom with my teachers and good friends, furniture conservators William Patrick Edwards and Patrice Lejeune, on cleaning solutions for a suite of rare (and very dirty) Louis XV gilt bronzes.

The cleaning problems they presented were complex. The delicate nature of the thin gold surface required a solution that would effectively remove stubborn grime without any mechanical action that might abrade the surface (including swab cleaning that can leave micro-scratches in the soft gold surface). The process of working on cleaning solutions together in real-time, with video feedback, enabled us to develop an excellent cleaning system.

I could design solutions on my computer 400 miles away using the Modular Cleaning Program, Patrice and Patrick prepared them, then gave me their observations on the cleaning results (did the surface feel tacky? was there a coating swelling or detaching? how did it look under different light?).

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With the new Modular Cleaning Program microemulsion module, and ultra-concentrated testing solutions coming out, I thought it might be a good time to open up conservation consultations more broadly.

The standard consultation rate is $100/30min, but if you’re a student or emerging professional special arrangements can be made. If your studio or institution is interested in an online lecture or class, this is a brief sample of topics I’ve covered in the past:

• Microemulsions & Nanostructured Fluids: Physical Chemistry, Surface Science, and Formulation

• Targeted Conservation Cleaning System Design

• Wooden Artifacts Conservation

• Conservation of Marquetry Furniture

• Chemistry of Cellulose & Natural Dyes

• Chemistry of Solvent & Protein Film Interactions

• Matte Paint Cleaning Methodologies

• Material Characterization Tests

If you or your institution have any questions on the new version of the MCP, or any other conservation problems I may be able to help with, just send me an email and we can set up a consultation, class, or lecture.

Pemulen TR-2 Emulsion: Indirect Method

This is the Indirect Method of preparing Pemulen TR-2 emulsions. I also demonstrate how to check the pH of the emulsion with an indicator dye and how to adjust the pH of the emulsion. I find this method to be far superior to the direct addition method.

The secret weapon for either method: a hand mixer. Mixing the Pemulen with an electric hand mixer will pretty much guarantee a successful emulsion, and they cost a lot less than $3,000+ overhead high-torque lab mixers.

1. In the direct method, Pemulen is added directly to the aqueous solution.

2. In the indirect method, Pemulen is dispersed in a solvent, which is then added to the aqueous solution.

3. This method works for all solvents except polar protic solvents (which mainly includes alcohols).

Standard Emulsions

This Pemulen TR-2 oil-in-water (o/w) emulsion was designed with the Modular Cleaning Program (MCP) developed by Chris Stavroudis to remove soiling materials ...

This Pemulen TR-2 oil-in-water (o/w) emulsion was designed with the Modular Cleaning Program (MCP) developed by Chris Stavroudis to remove soiling materials and decomposition products intermixed with aged plant-resin varnish on a wooden artifact. The advantage of an emulsion is that both water and solvents can be used simultaneously to solubilize intermixed residues of polar & non-polar materials.

Pemulen TR-2 is a blocked poly(acrylic acid)/polyacrylate copolymer/cross-polymer preparation capable of creating hydrophobic regions that act as emulsifiers, eliminating the need for a surfactant. Pemulen TR-2 at 1% (w/v) can be used from pH 6-9 and hold around 30-40% of the solvent phase. It has a chelating effect due to carboxylic acid groups in its poly(acrylic acid) structure. Triethanolamine (TEA) is an organic tertiary amine base that neutralizes the Pemulen TR-2. TEA has three alcohol groups enabling it to perform similarly to related alcohols and esterify & swell oil varnishes.

The aqueous component of the emulsion is the continuous phase. The Gamsol (ShellSol D38 refined to remove impurities/aromatics) is the 'oil' or dispersed phase. Citric acid acts as both the buffer and chelator. Citric acid has three pKas: 3.1, 4.7, and 6.4 with 6.4 generally being the one of interest to conservators. This indicates it will be an effective buffer from pH 5.4-7.4. I need a pH of 6.5 for this cleaning material, so citric acid is an excellent choice.

Disclaimer: do not attempt to use any of these specific cleaning systems. They are tailored to each object. Application in another context may permanently damage the object. These posts are meant to be educational only.

References:

Cremonesi, et al. “The Influence of Organic and Inorganic Alkalis on the Formulation and Properties of Pemulen TR-2 Gels.” Gels in the Conservation of Art , Archetype Publications Ltd, 2017, pp. 165–171.

Stavroudis, Chris. “Gels: Evolution in Practice.” Gels in the Conservation of Art, Archetype Publications Ltd, 2017, pp. 209–217.

Stavroudis, Chris, and Wolbers. “Aqueous Methods for the Cleaning of Paintings.” Conservation of Easel Paintings: Principles and Practice, Butterworth-Heinemann, 2012, pp. 500–523.