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Grafted polymer surfaces for dropwise condensation, and associated methods of use and manufacture

a polymer surface and dropwise condensation technology, applied in the field of grafted polymer surface, to achieve the effects of reducing thermal resistance, reducing drop shedding size, and reducing degradation ra

Inactive Publication Date: 2014-10-23
MASSACHUSETTS INST OF TECH
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

This patent describes articles and methods for creating thin, uniform polymer films on metal surfaces using a technique called iCVD. These films can be crosslinked and can reduce thermal resistance, drop shedding size, and degradation rate when exposed to steam. The patent also describes a method for using the polymer coated surface with a thermal interface material to improve thermal transfer efficiency in applications such as microprocessors and heatsinks. Annealing the polymer film can further improve its properties.

Problems solved by technology

C6 monomers undergo surface group reorganization, which is undesirable.

Method used

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  • Grafted polymer surfaces for dropwise condensation, and associated methods of use and manufacture
  • Grafted polymer surfaces for dropwise condensation, and associated methods of use and manufacture
  • Grafted polymer surfaces for dropwise condensation, and associated methods of use and manufacture

Examples

Experimental program
Comparison scheme
Effect test

experiment c

Film Characterization Experiment C

Surface Roughness Measurements

[0160]Surface roughness was measured using atomic force microscopy (AFM, MP3D-SA, Asylum) in tapping mode. The advancing and receding contact angles were measured using a goniometer (Model 590 Advanced, ramé-hart). The hysteresis was also measured during condensation on the grafted polymer sample as the difference between the receding and advancing ends of a drop immediately before departure. Contact angles during condensation on the silanized sample could not be measured due to the film covering the surface.

Dropwise Condensation Experiment A

Nucleation and Shedding Comparison

[0161]In addition to CAH, the dropwise condensation heat transfer depends on a number of complex factors including nucleation site density and population distribution. To investigate the behavior of these surfaces during condensation, saturated pure water vapor at 800 Pa was condensed while cooling the surface with a Peltier device to a supersaturat...

experiment b

Dropwise Condensation Experiment B

Aluminum Substrate Experiment

[0162]Commercial condensers are typically constructed using alloys of metals such as titanium, stainless steel, copper, and aluminum. To test a prototype that was most similar to an industrial condenser, a 40 nm film of p(PFDA-co-DVB) was grafted onto 50 mm diameter aluminum substrates via iCVD. The additional roughness imparted by the metal surface (RMS=118±33 nm) was apparent in the AFM height scans (shown in FIGS. 3a and 3b). As expected on a rougher surface in a Wenzel state, the CAH measured during condensation at 6.9 kPa was similar (37°±5°) and accordingly, the size of a departing drop (4.2±0.1 mm) was larger than that on a silicon substrate (as shown in FIG. 3c).

Dropwise Condensation Experiment C

Effect of Grafting

[0163]In this Example, coated substrates were tested for condensation performance in the apparatus described below and shown in FIG. 6. The flow loop of the test apparatus is shown in FIG. 7. Saturated s...

experiment d

Dropwise Condensation Experiment D

Film Thickness & Heat Transfer Coefficient

[0166]Referring now to FIG. 1a, monomer and initiator species are flowed into a reactor at controlled rates, where the monomer and initiator species encounter heated filaments and a cooled substrate, as shown in FIG. 1b. The locally heated zone around the filaments thermally cleaves the initiator species (tert-butyl peroxide, TBPO). The produced radical fragments initiate vinyl polymerization of the monomers absorbed on the surface, which is held at a lower temperature. The functional groups, such as the perfluorinated side chain of PFDA, are fully preserved after polymerization.

[0167]The film thickness is measured in-situ during deposition, so that the process can be stopped when the thickness reaches the desired value. In some embodiments, the iCVD copolymer layers are ultra-thin (˜40 nm), leading to an estimated contribution to total thermal resistance of less than 0.001%. To verify that the film thicknes...

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Abstract

Presented herein are articles and methods featuring substrates with thin, uniform polymeric films grafted (e.g., covalently bonded) thereupon. The resulting coating provides significant reductions in thermal resistance, drop shedding size, and degradation rate during dropwise condensation of steam compared to existing coatings. Surfaces that promote dropwise shedding of low-surface tension condensates, such as liquid hydrocarbons, are also demonstrated herein.

Description

RELATED APPLICATIONS[0001]This application claims priority to and the benefit of U.S. Provisional Patent Application No. 61 / 876,195, filed Sep. 10, 2013, U.S. Provisional Patent Application No. 61 / 874,941, filed Sep. 6, 2013, and U.S. Provisional Patent Application No. 61 / 765,679, filed Feb. 15, 2013, the contents of which are hereby incorporated by reference herein in their entireties.GOVERNMENT SUPPORT[0002]This invention was made with government support under Contract No. W911NF-07-D-0004 awarded by the Army Research Office. The government has certain rights in the invention.FIELD OF THE INVENTION[0003]This invention relates generally to grafted polymer surfaces and their use for enhanced heat transfer, improved dropwise condensation, and / or reduced adhesion of liquids and solids thereto.BACKGROUND OF THE INVENTION[0004]Vapors condense upon a surface if the surface is cooled below the saturation temperature at a given pressure. The condensed liquid phase may accumulate on the sur...

Claims

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Application Information

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IPC IPC(8): C09K5/00
CPCC09K5/00B05D1/60B05D3/02B05D5/08B05D5/083C09K5/14F28F13/182F28F19/04F28F2245/04Y10T428/1352Y10T428/24355Y10T428/24851Y10T428/265Y10T428/3154B05D3/0254B32B7/12B32B15/082B32B2307/302F28F13/04F28F21/06
Inventor PAXSON, ADAM T.YAGUE, JOSE L.VARANASI, KRIPA K.GLEASON, KAREN K.LIU, ANDONG
Owner MASSACHUSETTS INST OF TECH
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