inter-specific variation in adhesion

8/4/2019 Inter-Specific Variation in Adhesion

http://slidepdf.com/reader/full/inter-specific-variation-in-adhesion 1/15

Inter-specific variation in adhesion

strength of barnacles on foul-release

coatings

Teo, Serena Lay-Ming, Lim Chin-Sing & Sin Tsai-Min

Tropical Marine Science Institute

National University of Singapore

Singapore



Two major types of Commercial Antifouling Coatings:

1) Conventional Biocide based ablative coatings

2) Fouling release silicon elastomeric coatings



EXPERIMENT: Barnacle Adhesion on Intersleek 425• Panels were immersed at Singapore Test Site (Nov 05- )• 3 x Intersleek 425 panels x Front, Back

• panels were gently wiped clean then allowed to foul with barnacles

• Readings taken approx 3 weeks – 1 month later.

• 20-30 force gauge readings were taken for each facing of the panels

L-R: Amphibalanus (=Balanus)

• cirratus

• reticulatus• amphitrite



ASTM D 5618-94 :

Standard test method for measurement of barnacle adhesionstrength in shear

• Test surfaces were immersed according to ASTM D3623

• Only small barnacles 5- 20mm base diameter, at least 20mm away from edge,

not overgrown or in contact with other barnacles were selected.• The force gauge was placed at base of barnacle, and shear force applied

parallel to surface, at approx 4.5 N/s until the barnacle is detached.

• The force was recorded. If base is broken, test is invalid. At least 20-30

barnacles were tested for each panel facing.

• The barnacles were collected and returned to lab for identification. The area of

the base was calculated using a digitiser pad.

Swain et al. (2000) : California, Florida & Hawaii < < Italy, Singapore.

For Intersleek: Hawaii = 0.046MPa± 0.015 cf Singapore 0.125MPa±0.059



Barnacle Plaque

Plaque formation described by Wiegemann &

Watermann (2003) –abnormal concave shape base

plates filled with a highly hydrated adhesive plaque.

Likely to be part of a repair mechanism to bridge gap

between the base and substratum; at the expense of

cross-linking and lower cohesive strength

elasticity which is favourable for adhesion to flexibleelastic coatings.

Holm et al. 2005 – demonstrated difference in adhesive

properties of different genetic lines of barnacles

Wendt et al. 2006 – demonstrated lower criticalremoval stress associated with individuals with atypical

cupped base



Plaque Cover and Thickness

Aspect Ratio = Height / Diameter



Questions:

1. Does adhesion strength change over time?

2. Is there a difference in adhesion strength between

species of barnacles?

3. Is the difference in adhesion strength related todifferences in growth form (size, aspect ratio) or plaque

(cover, thickness)?



1. Does adhesion strength change over time?• Two way ANOVA with date, species vs calculated force: date F5,10=8.7,

p<0.0001; date x species F10,365=2.20, p<0.05)

• A. amphitrite – no significant difference in adhesion strength between

sampling dates (but sample size/individuals small?)

• A. reticulatus, A. cirratus – Post hoc analysis showed significant differences

among months

Adhesion Strength (MPa)

0.12

cirratus

0

0.02

0.04

0.06

0.08

0.1

Mar-06 Apr-06 Jun-06 Jul-06 Sep-06 Jun-07

C a l c f o r c e ( M P a )

reticulatus



Adhesion Strength (MPa)

0

0.02

0.04

0.06

0.08

0.1

0.12

Feb-06 Mar-06 May-06 Jul-06 Aug-06 Oct-06 Nov-06 Jan-07 Mar-07 Apr-07 Jun-07 Aug-07

C a l c f o r c e ( M P a )

c irra tu s re tic ula tu s

Adhesion

strength

0

10

20

30

40

50

60

70

80

Time

%

f o u l i n g o f b a r n a c l e s

Barnacle

monthly

recruitment



2. Is there a difference in adhesion strength betweenthe two species of barnacles?

A. cirratus A. reticulatus

0.062±0.032 (all data) 0.063±0.029 (all data)

0.092± 0.04 (Jul 06) 0.086 ±0.031 (Jul 06, Jun 07)

0.071±0.026 (Mar, Sep 06, Jun 07) 0.055 ±0.024 (rest of months)

0.037±0.02 (Apr, Jun 06)

• No difference if you average the whole data set

• But significant difference in adhesion strength for the two species

was recorded in some months (eg. April, June 06).



3a. Is the difference in adhesion

strength related to differences

in growth form (size, aspect

ratio)?

•Two way MANOVA detected significant effects on species and date with aspect ratio

F2,10=3.745, F5,10=2.481, p<0.005)

•Post-hoc Fisher LSDs detected significant differences in aspect ratio

Aspect Ratio (height:diameter)

0.3

0.35

0.4

0.45

0.5

0.55

.




3a. Is the difference in adhesion strength

related to differences in plaque (cover,

thickness)?

•Forward stepwise multiple regression was performed for each barnacle species with

calc force as dependent variable and av height, aspect ratio, plaque thickness and

cover as independent predictors

•Barnacle height is important (cf. aspect ratio – tall barnacles, lower adhesion

strength)

•Plaque cover consistently retained in regression equation for all 3 species

Species df1, df2 Regression

F

Regression

p

R2

term beta Term p

amphitrite 1,35 2.97 ns 7.8 Plcover

-0.28 ns

<0.05

cirratus 3,109 8.10 <0.001 16.0 Av ht -0.371 <0.0001

Plcover

-0.432 <0.01

Pl thick 0.26 0.09reticulatus 3,221 12.56 <0.0001 13.4 Av ht -0.213 <0.01

Plcover

-0.232 <0.001

aspect -0.16 <0.05



3

• For most part, A. reticulatus had higher plaque cover and

thickness than A. cirratus, except during peak settlement period in

both July 06 and Jun 07.

• For A. reticulatus, taller barnacles had more plaque cover and

thickness

0

1

2


A v P l a q u e C o v e r



SUMMARY OF RESULTS:

1. Adhesion strength fluctuated over time. This may be a result of fitness or

environmental parameters.

2. The effect may also be related to the morphology of barnacles in the sample.

3. Tall barnacles have lower adhesion strength, which may/may not be associated

to the presence of plaque.

. . .

cirratus (resulting in the presence of more smaller, tall individuals in the samplesthan A. cirratus??).

5. Increased plaque cover reduces adhesion strength.

6. When aspect ratio was similar between the 2 species, adhesion strength was

not significantly different even when the plaque cover was significantly different,suggesting that for this test, barnacle shape had a greater effect on adhesion

strength measurements than effects arising from plaque alone.



ACKNOWLEDGEMENTS

• Financial support from the US Office for Naval Research through grant N00014-

04-1-0789, and Collaborators from the ONR Coatings Program for their

assistance and good advice.

• Mr Mohammad Razali bin Duriat for field technical support,• Colleagues from the marine laboratory at Tropical Marine Science Institute for

their assistance during the project.

• The Republic of Singapore Yacht Club for generously hosting our field test site

.

inter-specific variation in adhesion

Documents