Table 1.

Central composite design arrangement and observed response.

Design Points	Coded Independent Variables				Response Values
	X1	X2	X3	X4	EE (%)	Size (nm)
1	−1	−1	−1	−1	23.6	135.2
2	1	−1	−1	−1	31.3	153.0
3	−1	1	−1	−1	65.3	183.5
4	1	1	−1	−1	65.6	170.1
5	−1	−1	1	−1	22.1	132.4
6	1	−1	1	−1	28.8	152.8
7	−1	1	1	−1	48.4	180.8
8	1	1	1	−1	30.0	138.9
9	−1	−1	−1	1	45.9	155.5
10	1	−1	−1	1	19.5	126.1
11	−1	1	−1	1	24.7	148.7
12	1	1	−1	1	21.9	179.6
13	−1	−1	1	1	44.3	143.6
14	1	−1	1	1	18.3	147.1
15	−1	1	1	1	43.6	147.8
16	1	1	1	1	43.0	130.8
17	−2	0	0	0	38.0	164.8
18	2	0	0	0	29.1	138.6
19	0	−2	0	0	19.2	134.8
20	0	2	0	0	44.3	157.5
21	0	0	−2	0	34.5	206.3
22	0	0	2	0	48.1	144.2
23	0	0	0	−2	21.2	172.7
24	0	0	0	2	25.9	127.0
25	0	0	0	0	19.5	142.9
26	0	0	0	0	23.6	119.6
27	0	0	0	0	14.9	122.5
28	0	0	0	0	19.6	124.8
29	0	0	0	0	24.8	127.0
30	0	0	0	0	26.7	133.1
31	0	0	0	0	28.1	129.7